Process for group III-IV semiconductor nanostructure synthesis and compositions made using same

ABSTRACT

Methods for producing nanostructures, particularly Group III-V semiconductor nanostructures, are provided. The methods include use of novel Group III and/or Group V precursors, novel surfactants, oxide acceptors, high temperature, and/or stable co-products. Related compositions are also described. Methods and compositions for producing Group III inorganic compounds that can be used as precursors for nanostructure synthesis are provided. Methods for increasing the yield of nanostructures from a synthesis reaction by removal of a vaporous by-product are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/475,772, filed Jun. 1, 2009, which is a divisional of U.S. patentapplication Ser. No. 11/178,257, filed Jul. 8, 2005, now U.S. Pat. No.7,557,028, which claims the benefit of U.S. Provisional PatentApplications No. 60/628,455 filed Nov. 15, 2004 and 60/591,987 filedJul. 28, 2004, each of which is incorporated by reference in itsentirety herein.

FIELD OF THE INVENTION

The invention is in the field of nanostructure synthesis. The inventionrelates to methods for producing nanostructures, particularly GroupIII-V semiconductor nanostructures. The invention also relates tocompositions useful in producing nanostructures, and to methods andcompositions for producing Group III inorganic compounds that can beused as precursors for nanostructure synthesis.

BACKGROUND OF THE INVENTION

Semiconductor nanostructures can be incorporated into a variety ofelectronic and optical devices, for example, photovoltaic devices andLEDs. The electrical and optical properties of such nanostructures vary,e.g., depending on their composition, shape, and size. Group III-Vsemiconductors, for example, exhibit a number of desirable electricalproperties such as low energy and direct band gap behaviors and highelectron mobility, as well as other desirable properties such as thermalstability.

Methods for simply and reproducibly producing Group III-V semiconductornanostructures, e.g., nanostructures of different sizes and/or shapes,are thus desirable. Among other aspects, the present invention providessuch methods. A complete understanding of the invention will be obtainedupon review of the following.

SUMMARY OF THE INVENTION

Methods for producing nanostructures, particularly Group III-Vsemiconductor nanostructures, are provided. The methods include, e.g.,use of novel Group III and/or Group V precursors, novel surfactants,sacrificial oxide acceptors, high temperature, and/or stableco-products. Related compositions are also described. Methods andcompositions for producing Group III inorganic compounds that can beused as precursors for nanostructure synthesis are provided. Methods forincreasing the yield of nanostructures from a synthesis reaction byremoval of a vaporous by-product are also described.

A first general class of embodiments provides methods for production ofGroup III-V semiconductor nanostructures. In the methods, a firstprecursor and a second precursor are provided, and the first and secondprecursors are reacted to produce the nanostructures. The firstprecursor comprises a trisubstituted Group V atom, other than a) atrialkyl substituted Group V atom comprising an unbranched andunsubstituted alkyl group, b) an H₃ substituted Group V atom, c) anH₂alkyl substituted Group V atom comprising an unbranched andunsubstituted alkyl group, d) an Halkyl₂ substituted Group V atomcomprising an unbranched and unsubstituted alkyl group, or e) atris(trialkylsilyl) substituted Group V atom. The second precursorcomprises a Group III atom. The Group V atom can be any atom selectedfrom Group V of the periodic table of the elements. In a preferred classof embodiments, the Group V atom is N, P, As, Sb, or Bi.

In one class of embodiments, the first precursor is a Group Vorganometallic compound. In one aspect, the first precursor comprises aGroup V atom substituted with three unsaturated groups. For example, thefirst precursor can be triallylphosphine, trivinylphosphine,tributadienylphosphine, trialkylethynylphosphine,trialkylethenylphosphine, tri(4-phenylethynyl)phosphine, ortrialkylphenylethynylphosphine. As another example, the first precursorcan include a Group V atom substituted with three furyl or furfurylgroups; e.g., the first precursor can be tri-2-furylphosphine ortri-2-furfurylphosphine.

In one class of embodiments, the first precursor comprises a triacylsubstituted Group V atom. The acyl group can be, e.g., unsubstituted orsubstituted. For example, the first precursor can be a triacylphosphineor a triacylarsine, e.g., tribenzoylphosphine, trialkylbenzoylphosphine,trihexylbenzoylphosphine, trialkoylphosphine, or trihexoylphosphine. Thesecond precursor optionally includes three unsaturated groups,substituting the Group III atom.

In a related class of embodiments, the first precursor comprises atriaryl substituted Group V atom. The aryl group can be, e.g.,unsubstituted or substituted. In one class of example embodiments, thefirst precursor comprises a tribenzyl substituted Group V atom; forexample, the first precursor can be tribenzylphosphine ortribenzylarsine.

In another related class of embodiments, the first precursor comprises aGroup V atom substituted with three carboxamide groups. Thus, forexample, the first precursor can be a tricarboxamide phosphine, e.g.,N,N,N,N,N,N-hexaethylphosphine tricarboxamide.

In another class of embodiments, the first precursor comprises atrialkyl substituted Group V atom comprising a substituted and/orbranched alkyl group. For example, the first precursor can include atri-t-butyl substituted Group V atom; e.g., the first precursor can betri-t-butylphosphine.

In certain embodiments, the first precursor is a Group V inorganiccompound. For example, in one class of embodiments, the first precursorcomprises a Group V atom substituted with three carboxylate moieties orwith three phosphinate moieties. In one embodiment, the Group V atom isP such that the first precursor is a phosphite ester. The secondprecursor optionally also includes three carboxylate moieties or withthree phosphinate moieties, substituting the Group III atom.

The first precursor can be used in combination with essentially anysuitable second precursor, whether previously known in the art ordescribed herein. The Group III atom can be any atom selected from GroupIII of the periodic table of the elements. In a preferred class ofembodiments, the Group III atom is B, Al, Ga, In, or Tl.

In one aspect, the second precursor is a Group III inorganic compound.In one class of embodiments, the second precursor is a Group III halide.Thus, in this class of embodiments, the second precursor is YZ3, where Yis a Group III atom (e.g., B, Al, Ga, In, or Tl) and Z is a halogen atom(e.g., F, Cl, Br, I, or At).

In another class of embodiments, the second precursor comprises one ormore phosphonate, phosphinate, carboxylate, sulfonate, and/or boronatemoieties bonded to the Group III atom. For example, the second precursorcan comprise a bi- or tri-substituted Group III atom (e.g., atricarboxylate, bi- or tri-phosphonate, or triphosphinate substitutedGroup III atom). Thus, in one class of embodiments, the second precursoris Y(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, or Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. The alkyl or aryl group can be, e.g., substituted orunsubstituted. For example, the second precursor can be an indiumphosphonate or indium carboxylate (e.g., indium triacetate or indiumtristearate).

In yet another class of embodiments, the second precursor is a Group IIImetal oxide. For example, the second precursor can be indium oxide orgallium oxide. As another example, the second precursor can be a GroupIII alkoxy or Group III aryloxy (e.g., a Group III phenoxy, e.g., indiumphenoxy).

In one class of embodiments, instead of being a Group III inorganiccompound, the second precursor is a Group III organometallic compound.For example, the second precursor can be an alkyl metal or a trialkylmetal, e.g., trimethyl indium or triethyl indium. In one aspect, thesecond precursor comprises a Group III atom substituted with threeunsaturated groups. For example, the second precursor can be triallylindium, trivinyl indium, tributadiene indium, trialkylethynyl indium,trialkylethenyl indium, tri-4-phenylethynyl indium, ortrialkylphenylethynyl indium. In other embodiments, the second precursorcomprises a Group III atom substituted with three cyclic ketone groups;for example, the second precursor can be tris-alpha-cyclohexanone indium(III). In yet other embodiments, the second precursor comprises a GroupIII atom substituted with three cyclopentadienyl or substitutedcyclopentadienyl groups. For example, the second precursor can be anindium tris-Cp compound or an indium tris-(substituted Cp) compound, forexample, tris-cyclopentadienyl indium(III) or tris(n-hexylcyclopentadienyl) indium(III).

In one class of embodiments, the first precursor comprises atrisubstituted Group V atom where the substituents are dienes, while thesecond precursor includes a trisubstituted Group III atom where thesubstituents are dienophiles. In a related class of embodiments, thefirst precursor comprises a trisubstituted Group V atom where thesubstituents are dienophiles while the second precursor includes atrisubstituted Group III atom where the substituents are dienes.

The first and second precursors are typically reacted in the presence ofat least one surfactant. For example, the precursors can be reacted inthe presence of a first surfactant, a second surfactant, or a mixture offirst and second surfactants. Suitable first surfactants include, butare not limited to, tri-n-alkyl phosphines (e.g., TOP and tri-n-butylphosphine (TBP), and C12-C30 tri-n-alkyl phosphines, e.g., tri-n-dodecylphosphine or tri-n-hexadecyl phosphine), tri-n-alkyl phosphine oxides(e.g., TOPO), alkyl amines (e.g., monoalkyl amines and bialkyl amines,or trialkyl amines such as trioctylamine), and alkyl- and/oraryl-thiols. Suitable first surfactants also include unsaturated Group Vderivatives; the first surfactant can comprise a Group V atomsubstituted with three unsaturated groups (e.g., alkenyl or alkynylgroups). Examples include trisalkylphenylethynylphosphines, e.g.,tri(ethynylbenzene-hexyl)phosphine,tris(ethynylbenzene-pentyl)phosphine, and the other unsaturatedphosphines noted herein.

Suitable second surfactants include, but are not limited to, alkylamines (e.g., mono-, bi-, and tri-alkyl amines; typically, the firstsurfactant is not also an alkyl amine) and phosphonic acids (e.g., aC2-30 alkylphosphonic acid), phosphinic acids (e.g., a C2-30bialkylphosphinic acid), carboxylic acids (e.g., a C2-30 alkylcarboxylicacid), boronic acids, and sulfonic acids, as well as deprotonated formsor condensates thereof.

In one class of embodiments, the first and second precursors are reactedin the presence of a non-coordinating solvent, e.g., an alkane or analkene, e.g., hexadecane, octadecane, octadecene, phenyldodecane,phenyltetradecane, or phenylhexadecane. In one class of embodiments, thefirst and second precursors are reacted in the presence of thenon-coordinating solvent and a first and/or second surfactant (e.g., anyof those described herein). For example, the first and second precursorscan be reacted in the presence of the non-coordinating solvent (e.g.,phenylhexadecane) and a carboxylic acid (e.g., stearic acid), andoptionally also in the presence of a sacrificial oxide acceptor (e.g.,triphenylphosphine).

Using a mixture of surfactants, varying the ratio of the surfactant(s)to the precursors, and/or varying the ratio of the precursors to eachother permits the shape and/or size of the resulting nanostructures tobe controlled. Thus, in one class of embodiments, reacting the first andsecond precursors comprises reacting the first and second precursors inthe presence of at least a first surfactant and a second surfactant,whereby the shape of the nanostructures produced is capable of beingcontrolled by adjusting the ratio of the first and second surfactants.For example, the ratio of the first and second surfactants can beadjusted to produce substantially spherical nanocrystals, nanorods,branched nanostructures, and/or nanotetrapods. Additional surfactantscan also be used to help control the shape of the resultingnanocrystals. Thus, in some embodiments, the first and second precursorsare reacted in the presence of a first surfactant, a second surfactant,and a third surfactant.

In a related class of embodiments, reacting the first and secondprecursors comprises reacting the first and second precursors in thepresence of a second surfactant, whereby the shape of the nanostructuresproduced is capable of being controlled by adjusting the ratio of thesecond surfactant and the first or second precursor. For example, theratio of the second surfactant and the first or second precursor can beadjusted to produce substantially spherical nanocrystals, nanorods,branched nanostructures, and/or nanotetrapods.

In another related class of embodiments, the ratio of the first andsecond precursors is adjusted to control the shape of the nanostructuresproduced. As for the embodiments above, the ratio of the first andsecond precursors can be adjusted to produce, e.g., substantiallyspherical nanocrystals, nanorods, branched nanostructures, and/ornanotetrapods.

Alternatively or in addition, the temperature can be controlled tocontrol the shape and/or size distribution of the resultingnanostructures. Thus, in one class of embodiments, reacting the firstand second precursors to produce the nanostructures includes heating atleast one surfactant (e.g., a first and a second surfactant) to a firsttemperature; contacting the first and second precursors and the heatedsurfactant, whereby the first and second precursors react to form nucleicapable of nucleating nanostructure growth; and maintaining the firstand second precursors, the surfactant, and the nuclei at a secondtemperature. The second temperature permits growth of the nuclei toproduce the nanostructures, whereby the first and second precursorsreact to grow the nanostructures from the nuclei. The first (nucleation)temperature is typically greater than the second temperature, e.g., byabout 40-80° C., about 20-40° C., about 10-20° C., about 5-10° C., orabout 0-5° C.; the first and second temperatures can, however, be equal,or the first temperature can be less than the second temperature (e.g.,by about 40-80° C., about 20-40° C., about 10-20° C., about 5-10° C., orabout 0-5° C.). In some embodiments, the first temperature is at least300° C., at least 330° C., at least 360° C., at least 380° C., at least400° C., or at least 420° C. In some embodiments, the second temperatureis at least 250° C., at least 275° C., at least 300° C., at least 320°C., at least 340° C., at least 360° C., at least 380° C., at least 400°C., or at least 420° C.

Yield of nanostructures from the reaction is optionally increased byremoval of one or more by-products during the reaction. Thus, in someembodiments, the first and second precursors react to produce thenanostructures and a by-product that has a boiling point or sublimationtemperature that is less than the second temperature. The methodsinclude removing at least a portion of the by-product as a vapor.

The precursors can be added either simultaneously or sequentially to areaction vessel in which nanostructure synthesis is performed. Thus, inone class of embodiments, reacting the first and second precursors toproduce the nanostructures includes contacting the first and secondprecursors, which form a Group III-V complex. The Group III-V complex isthen reacted to produce the nanostructures. The complex is optionallyisolated after it is formed.

In one class of embodiments, the first and second precursors are reactedin the presence of a sacrificial oxide acceptor, e.g., a pi-acid such astriphenylphosphine or a substituted triphenylphosphine.

The nanostructures produced by the methods can be essentially any shapeand/or size. For example, the resulting nanostructures can includenanocrystals, substantially spherical nanocrystals, nanorods, branchednanostructures, and/or nanotetrapods. Similarly, the nanostructures cancomprise essentially any Group III-V semiconductor, including, but notlimited to, InN, InP, InAs, InSb, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs,or AlSb.

Another general class of embodiments provides high temperature methodsfor production of Group III-V semiconductor nanostructures. In themethods, a first precursor and a second precursor are provided. Thefirst and second precursors are reacted at a first temperature of atleast 300° C. to produce the nanostructures. The first precursorcomprises a trisubstituted Group V atom, where the three substituents onthe Group V atom are independently any alkyl group or hydrogen. Thesecond precursor comprises a Group III atom. The first temperature isoptionally at least 330° C., at least 360° C., at least 380° C., atleast 400° C., or at least 420° C.

The first precursor can include an H₃ substituted Group V atom, anH₂alkyl substituted Group V atom, or an Halkyl₂ substituted Group Vatom. In a preferred class of embodiments, the first precursor comprisesa trialkyl substituted Group V atom. The alkyl group can be, e.g.,substituted or unsubstituted and/or branched or unbranched (linear). Forexample, the first precursor can comprise a trimethyl substituted GroupV atom, a triethyl substituted Group V atom, or a tri-t-butylsubstituted Group V atom. Specific examples of first precursors include,but are not limited to, trimethylphosphine, triethylphosphine, andtri-t-butylphosphine.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, second precursors, removal of by-product to increasenanostructure yield, use of first and/or second surfactants, andcontrolling nanostructure shape by adjusting the ratio of the first andsecond surfactants, the ratio of the second surfactant and the first orsecond precursor, and/or the ratio of the first and second precursors.It is worth noting that the molar ratio of the first precursor to thesecond precursor can be varied; for example, the first precursor can beprovided at a molar ratio of at least 1:1, at least 2:1, at least 4:1,at least 8:1, or at least 12:1 with respect to the second precursor.

Yet another general class of embodiments also provides methods forproduction of Group III-V semiconductor nanostructures. In the methods,a first precursor and a second precursor are provided, and the first andsecond precursors are reacted to produce the nanostructures. The firstprecursor comprises a Group V atom. The second precursor is either aGroup III inorganic compound other than a Group III halide (e.g., InCl₃)or a Group III acetate (e.g., InAc₃), or a Group III organometalliccompound other than a trialkyl substituted Group III atom comprising anunbranched and unsubstituted alkyl group.

The Group III atom can be any atom selected from Group III of theperiodic table of the elements. In a preferred class of embodiments, thesecond precursor comprises B, Al, Ga, In, or Tl as the Group III atom.

In one aspect, the second precursor is a Group III inorganic compound(e.g., a compound in which the Group III atom is directly bonded to atleast one oxygen atom or other heteroatom, e.g., nitrogen).

In one class of embodiments, the second precursor is a Group IIIinorganic compound comprising one or more phosphonate, phosphinate,carboxylate, sulfonate, and/or boronate moieties bonded to a Group IIIatom. For example, the second precursor can comprise a bi- ortri-substituted Group III atom (e.g., a tricarboxylate, bi- ortri-phosphonate, or triphosphinate substituted Group III atom). Thus, inone class of embodiments, the Group III inorganic compound isY(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, or Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. The alkyl or aryl group can be, e.g., substituted orunsubstituted. For example, the second precursor can be an indiumphosphonate or indium carboxylate other than indium triacetate (e.g.,indium tristearate).

In another class of embodiments, the Group III inorganic compound is aGroup III metal oxide. For example, the Group III inorganic compound canbe indium oxide or gallium oxide. As another example, the Group IIIinorganic compound can be a Group III alkoxy or Group III aryloxy (e.g.,a Group III phenoxy, e.g., indium phenoxy).

In another aspect, instead of being a Group III inorganic compound, thesecond precursor is a Group III organometallic compound. In one aspect,the second precursor comprises a Group III atom substituted with threeunsaturated groups. For example, the second precursor can be triallylindium, trivinyl indium, tributadiene indium, trialkylethynyl indium,trialkylethenyl indium, tri-4-phenylethynyl indium, ortrialkylphenylethynyl indium. In one class of embodiments, the secondprecursor comprises a Group III atom substituted with three cyclicketone groups; for example, the second precursor can betris-alpha-cyclohexanone indium (III). In other embodiments, the secondprecursor comprises a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups. For example,the second precursor can be an indium tris-Cp compound or an indiumtris-(substituted Cp) compound, for example, tris-cyclopentadienylindium(III) or tris(n-hexyl cyclopentadienyl) indium(III).

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, first precursors, non-coordinating solvents, sacrificial oxideacceptors, removal of by-product to increase nanostructure yield, use offirst and/or second surfactants, and controlling nanostructure shape byadjusting the ratio of the first and second surfactants, the ratio ofthe second surfactant and the first or second precursor, and/or theratio of the first and second precursors.

Another general class of embodiments provides methods of producing aGroup III inorganic compound. In the methods, a first reactant and asecond reactant are provided and reacted to produce the Group IIIinorganic compound. In some embodiments, the first reactant is a GroupIII halide, e.g., YZ₃, where Y is B, Al, Ga, In, or Tl and Z is F, Cl,Br, I, or At. In other embodiments, the first reactant comprises atrialkyl substituted Group III atom (e.g., trialkyl indium, e.g.,trimethyl indium). The second reactant is an acid, e.g., a phosphonicacid, a phosphinic acid, a carboxylic acid (e.g., stearic acid), asulfonic acid, or a boronic acid.

The resulting Group III inorganic compound thus, in certain embodiments,comprises one or more phosphonate, phosphinate, and/or carboxylatemoieties bonded to the Group III atom. Examples of such compoundsinclude, but are not limited to, Y(alkylcarboxylate)₃,Y(arylcarboxylate)₃, Y(alkylphosphonate)₃, Y(arylphosphonate)₃,Y(alkylphosphonate)₂, Y(arylphosphonate)₂, Y(bialkylphosphinate)₃, andY(biarylphosphinate)₃, where Y is B, Al, Ga, In, or Tl. For example, theGroup III inorganic compound can be indium phosphonate or indiumcarboxylate (e.g., indium tristearate).

The second reactant is typically provided at a molar ratio of about 3:1with respect to the first reactant (e.g., about 2.8-3.2, about 2.9-3.1,or about 2.95-3.05). In other embodiments, the second reactant isprovided at a molar ratio of more than 3:1 with respect to the firstreactant.

The resulting Group III inorganic compound is optionally used as aprecursor in a nanostructure synthesis reaction. Thus, in one class ofembodiments, the methods include providing a first precursor comprisinga Group V atom and reacting the Group III inorganic compound and thefirst precursor to produce Group III-V semiconductor nanostructures. TheGroup III inorganic compound is optionally substantially isolated fromany unreacted first reactant and/or second reactant prior to itsreaction with the first precursor.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first precursors.

Another general class of embodiments provides high-temperature methodsfor production of Group III-V semiconductor nanostructures. In themethods, one or more surfactants, a first precursor comprising a Group Vatom, and a second precursor comprising a Group III atom are provided.The one or more surfactants are heated to a first temperature. The firstand second precursors and the one or more heated surfactants arecontacted, and the first and second precursors react to form nucleicapable of nucleating nanostructure growth. The first and secondprecursors, the one or more surfactants, and the nuclei are maintainedat a second temperature which permits growth of the nuclei to producethe nanostructures; the first and second precursors react to grow thenanostructures from the nuclei. The first temperature is at least 360°C. and/or the second temperature is at least 300° C.

For example, the first temperature can be at least 380° C., at least400° C., or at least 420° C. Similarly, the second temperature can be atleast 330° C., at least 360° C., at least 380° C., at least 400° C., orat least 420° C. The first temperature can be greater than (or lessthan) the second temperature, e.g., by about 40-80° C., about 20-40° C.,about 10-20° C., about 5-10° C., or about 0-5° C., or the first andsecond temperatures can be equal. In a preferred class of embodiments,each of the one or more surfactants has a boiling point that is greaterthan the first and second temperatures.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, removal of by-product to increase nanostructure yield, GroupIII and V atoms, first and second precursors, use of first and/or secondsurfactants, and controlling nanostructure shape by adjusting the ratioof the first and second surfactants, the ratio of the second surfactantand the first or second precursor, and/or the ratio of the first andsecond precursors. It is worth noting that, in one class of embodiments,the first surfactant is a tri-n-alkyl phosphine or a tri-n-alkylphosphine oxide, for example, a C12-C30 tri-n-alkyl phosphine (e.g.,tri-n-dodecyl phosphine or tri-n-hexadecyl phosphine).

Yet another general class of embodiments provides methods for productionof Group III-V semiconductor nanostructures. In the methods, a firstprecursor comprising a Group V atom and a second precursor comprising aGroup III atom are provided and reacted to produce the nanostructuresand at least one co-product. In one class of embodiments, the co-productis an ester, a ketone, or an ether.

Reaction of a variety of combinations of first and second precursorsresults in formation of an ether, ketone, or ester. For example, whenthe first precursor comprises a trialkyl substituted Group V atom andthe second precursor comprises a tricarboxylate substituted Group IIIatom, the co-product can be an ester. As another example, the firstprecursor can comprise a triacyl substituted Group V atom, the secondprecursor a Group III atom substituted with three cyclic ketone groups(e.g., tris-alpha-cyclohexanone indium (III)), and the co-product anester. As yet another example, the first precursor can comprise atriacyl substituted Group V atom, the second precursor a tris-Cp ortris-(substituted Cp) Group III atom (e.g., an indium tris-Cp ortris-(substituted Cp) compound, e.g., tris-cyclopentadienyl indium(III)or tris(n-hexyl cyclopentadienyl) indium(III)), and the co-product aketone.

The methods optionally include substantially purifying thenanostructures away from the co-product (e.g., prior to their use orincorporation into an optoelectronic device, a nanocomposite, or thelike).

In one aspect, the invention provides methods for production ofnanostructures that can, e.g., increase yield of nanostructures fromnanostructure synthesis reactions through removal of a vapor by-product.In the methods, one or more precursors are provided and reacted at areaction temperature (e.g., a nanostructure growth temperature) toproduce the nanostructures and at least one by-product. The by-producthas a boiling point or sublimation temperature that is less than thereaction temperature. At least a portion of the by-product is removed asa vapor. Removal of the by-product pushes the reaction equilibriumtoward making more nano structures.

The nanostructures can be of essentially any type and/or composition.For example, the nanostructures can be semiconductor nanostructures,e.g., Group II-VI semiconductor nanostructures, Group III-Vsemiconductor nanostructures, Group IV semiconductor nanostructures,metal nanostructures, or metal oxide nanostructures.

In one class of embodiments, the one or more precursors comprise a firstprecursor comprising a group VI atom and a second precursor comprising agroup II atom, or a first precursor comprising a group V atom and asecond precursor comprising a group III atom. The resultingnanostructures can comprise, e.g., ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe,HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS,BaSe, BaTe, InN, InP, InAs, InSb, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs,or AlSb.

A number of precursors and reaction temperatures can be selected suchthat the by-product formed has a boiling point or sublimationtemperature less than the reaction temperature. For example, in oneclass of embodiments, at least two precursors are reacted to form GroupIII-V semiconductor nanostructures. The first precursor comprises atrialkyl or triaryl substituted Group V atom, the second precursor is aGroup III halide, and the by-product is thus an alkyl or aryl halide.Preferably, the Group V atom is N, P, As, Sb, or Bi, and the Group IIIhalide comprises B, Al, Ga, In, or Tl and F, Cl, Br, I, or At. Exampleby-products include, but are not limited to, chlorooctane, bromooctane,benzylbromide, benzyliodide, or benzylchloride. In one exampleembodiment, the first precursor is TOP, the second precursor is InCl₃,and the by-product is chlorooctane. Essentially all of the featuresnoted above apply to these embodiments as well, as relevant; e.g., fortypes and composition of nanostructures produced, inclusion ofsurfactant(s), precursors, and the like.

Methods and compositions including surfactants of the invention (e.g.,tri-unsaturated Group V derivatives) form a feature of the invention.Thus, one general class of embodiments provides methods for productionof nanostructures. In the methods, a surfactant comprising a Group Vatom substituted with three unsaturated groups and one or moreprecursors are provided. The one or more precursors are reacted in thepresence of the surfactant to produce the nanostructures. In one classof embodiments, the nanostructures are Group III-V semiconductornanostructures; in this class of embodiments, the one or more precursorscan, e.g., include a first precursor comprising a Group V atom and asecond precursor comprising a Group III atom.

The three unsaturated groups on the Group V atom in the surfactantoptionally comprise alkenyl or alkynyl groups. Thus, for example, thesurfactant can be a trisalkylphenylethynylphosphine, e.g.,trisalkylphenylethynylphosphine or tri(ethynylbenzene-hexyl)phosphine.

Compositions related to the methods are another feature of theinvention. Thus, one general class of embodiments provides a compositionincluding a first precursor and a second precursor. The first precursorcomprises a trisubstituted Group V atom, other than a) a trialkylsubstituted Group V atom comprising an unbranched and unsubstitutedalkyl group, b) an H₃ substituted Group V atom, c) an H₂alkylsubstituted Group V atom comprising an unbranched and unsubstitutedalkyl group, d) an Halkyl₂ substituted Group V atom comprising anunbranched and unsubstituted alkyl group, or e) a tris(trialkylsilyl)substituted Group V atom. The second precursor comprises a Group IIIatom.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first and second precursors,non-coordinating solvents, sacrificial oxide acceptors, and first and/orsecond surfactants. It is worth noting that the composition optionallyincludes one or more nanostructures comprising the Group III atom andthe Group V atom.

A related general class of embodiments provides a composition thatincludes a first precursor and a second precursor, where the temperatureof the composition is at least 300° C. (e.g., at least 330° C., at least360° C., at least 380° C., at least 400° C., or at least 420° C.). Thefirst precursor comprises a trisubstituted Group V atom, where the threesubstituents on the Group V atom are independently any alkyl group orhydrogen. The second precursor comprises a Group III atom.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first and second precursors,non-coordinating solvents, sacrificial oxide acceptors, and first and/orsecond surfactants. It is worth noting that, in one class ofembodiments, the first surfactant is a tri-n-alkyl phosphine, forexample, TOP, TBP, or a C12-C30 tri-n-alkyl phosphine (e.g.,tri-n-dodecyl phosphine or tri-n-hexadecyl phosphine). It is also worthnoting that the molar ratio of the first precursor to the secondprecursor can be varied; for example, the first precursor can be presentat a molar ratio of at least 1:1, at least 2:1, at least 4:1, at least8:1, or at least 12:1 with respect to the second precursor. Thecomposition optionally includes one or more nanostructures comprisingthe Group III atom and the Group V atom.

Another general class of embodiments provides a composition including afirst precursor comprising a Group V atom and a second precursor. Thesecond precursor is either a Group III inorganic compound other than aGroup III halide (e.g., InCl₃) or a Group III acetate (e.g., InAc₃), ora Group III organometallic compound other than a trialkyl substitutedGroup III atom comprising an unbranched and unsubstituted alkyl group.In certain embodiments, second precursors of the invention optionallyexclude any trialkyl substituted Group III atom.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first and second precursors,non-coordinating solvents, sacrificial oxide acceptors, and first and/orsecond surfactants. It is worth noting that the composition optionallyincludes one or more nanostructures comprising the Group III atom andthe Group V atom.

Another general class of embodiments provides a composition that can beused, for example, for producing a Group III inorganic compound. Thecomposition includes a first reactant and a second reactant. In someembodiments, the first reactant is a Group III halide, e.g., YZ₃, whereY is B, Al, Ga, In, or Tl and Z is F, Cl, Br, I, or At. In otherembodiments, the first reactant comprises a trialkyl substituted GroupIII atom (e.g., trialkyl indium, e.g., trimethyl indium). The secondreactant is an acid, e.g., a phosphonic acid, a phosphinic acid, acarboxylic acid (e.g., stearic acid), a sulfonic acid, or a boronicacid.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first and second reactants, Group IIIinorganic compounds, and the like. It is worth noting that thecomposition optionally includes a first precursor, a nanostructure,and/or the like.

Yet another general class of embodiments provides a compositioncomprising one or more surfactants, a first precursor comprising a GroupV atom, and a second precursor comprising a Group III atom. Thetemperature of the composition is at least 360° C. (e.g., at least 380°C., at least 400° C., or at least 420° C.). Each of the one or moresurfactants preferably has a boiling point that is greater than thetemperature of the composition.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first and second precursors, surfactants,and the like. It is worth noting that the composition optionallyincludes one or more nanostructures comprising the Group III atom andthe Group V atom.

Another general class of embodiments provides a composition comprising afirst precursor comprising a Group V atom, a second precursor comprisinga Group III atom, a nanostructure comprising the Group III atom and theGroup V atom, and a co-product. In one class of embodiments, theco-product is an ester, a ketone, or an ether. The nanostructure and theco-product were produced by reaction of the precursors.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for first and second precursors, co-products,composition of the nanostructures, and the like.

Another general class of embodiments provides a composition including asurfactant comprising a Group V atom substituted with three unsaturatedgroups and one or more precursors. The composition optionally alsoincludes one or more nanostructures, e.g., Group III-V semiconductornano structures. The one or more precursors can, e.g., include a firstprecursor comprising a Group V atom and a second precursor comprising aGroup III atom.

Essentially all of the features noted above apply to this embodiment aswell, as relevant. For example, the three unsaturated groups on theGroup V atom in the surfactant optionally comprise alkenyl or alkynylgroups. Thus, for example, the surfactant can be atrisalkylphenylethynylphosphine, e.g., trisalkylphenylethynylphosphineor tri(ethynylbenzene-hexyl)phosphine.

Nanostructures (including, but not limited to, nanocrystals,substantially spherical nanocrystals, nanorods, branched nanostructures,or nanotetrapods) produced by any of the methods herein form anotherfeature of the invention. One general class of embodiments provides ananostructure comprising a Group III-V semiconductor. The nanostructureis substantially free of metallic noble, Group Ib, Group IIb, GroupIIIb, and transition metal elements, and is optionally substantiallyfree of any metallic metal element. In one class of embodiments, thenanostructure is a branched nanostructure or a nanostructure having anaspect ratio greater than about 1.2, and the nanostructure has awurtzite crystal structure or a zinc blende-wurtzite mixed crystalstructure. For example, in one class of embodiments, the nanostructureis a nanotetrapod. In another class of embodiments, the nanostructure isa nanorod having an aspect ratio greater than about 1.2, greater thanabout 1.5, greater than about 2, greater than about 3, or greater thanabout 5.

The Group III-V semiconductor typically comprises a first atom selectedfrom the group consisting of N, P, As, Sb, and Bi and a second atomselected from the group consisting of B, Al, Ga, In, and Tl.

The nanostructures are optionally substantially free of Si, phosphonicacid, phosphinic acid, carboxylic acid, tri-n-alkyl phosphines and/ortri-n-alkyl phosphine oxides. In certain embodiments, the nanostructureshave a sulfonic acid, or a boronic acid, or a deprotonated form or acondensate thereof, associated with a surface of the nanostructures. Inother embodiments, the nanostructures have a carboxylic acid or adeprotonated form or a condensate thereof, and/or a surfactantcomprising a Group V atom substituted with three unsaturated groups,associated with a surface of the nanostructures.

Another general class of embodiments provides a nanostructure comprisinga Group III-V semiconductor, the nanostructure being a tetrahedralnanostructure. In one class of embodiments, the nanostructure has anedge at least 10 nm in length (e.g., at least 12 nm, at least 15 nm, orat least 20 nm). All six edges are optionally at least 10 nm in length.The nanostructure can be, e.g., a nanocrystal, and can have a zincblende crystal structure. Essentially all of the features noted aboveapply to this embodiment as well, as relevant; e.g., for composition ofthe nanostructure. Devices (e.g., photovoltaic devices or otheropto-electronic devices) including nanostructures of the invention arealso a feature of the invention.

Compositions including nanostructures and one or more Group IIIprecursor, Group V precursor, and/or surfactant of the invention arealso a feature of the invention. Thus, one general class of embodimentsprovides a composition that includes one or more nanostructures (e.g.,Group III-V semiconductor nanostructures) having a surfactant associated(covalently or non-covalently) with a surface thereof. The surfactantcomprises a Group V atom substituted with three unsaturated groups,e.g., alkenyl or alkynyl groups. Essentially all of the features notedabove apply to this embodiment as well, as relevant; e.g., for types andcomposition of nanostructures, types of surfactant, and the like. Forexample, the surfactant can be a trisalkylphenylethynylphosphine, e.g.,trisalkylphenylethynylphosphine or tri(ethynylbenzene-hexyl)phosphine.

Another general class of embodiments provides a composition thatincludes one or more Group III-V semiconductor nanostructures and afirst precursor of the invention. For example, the first precursor cancomprise a Group V atom substituted with three unsaturated groups, atriacyl substituted Group V atom, a Group V atom substituted with threecarboxamide groups, a triaryl substituted Group V atom, or a Group Vatom substituted with three carboxylate moieties or with threephosphinate moieties, for example, any such precursors described herein.For example, the first precursor can be triallylphosphine,trivinylphosphine, tributadienylphosphine, trialkylethynylphosphine,trialkylethenylphosphine, tri(4-phenylethynyl)phosphine,trialkylphenylethynylphosphine, a triacylphosphine, tribenzoylphosphine,trialkylbenzoylphosphine, trihexylbenzoylphosphine, trialkoylphosphine,trihexoylphosphine, a tricarboxamide phosphine,N,N,N,N,N,N-hexaethylphosphine tricarboxamide, tribenzylphosphine, ortribenzylarsine. As another example, the first precursor can include aGroup V atom substituted with three furyl or furfuryl groups; e.g., thefirst precursor can be tri-2-furylphosphine or tri-2-furfurylphosphine.As yet another example, the first precursor can be a phosphite ester.The composition optionally includes a second precursor, a firstsurfactant, a second surfactant, and/or a non-coordinating solvent.Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructures,second precursors, first and second surfactants, solvents, sacrificialoxide acceptors, and the like.

Yet another general class of embodiments provides a composition thatincludes one or more Group III-V semiconductor nanostructures and asecond precursor of the invention. For example, the second precursor cancomprise a Group III atom which is directly bonded to at least oneoxygen atom; one or more phosphonate, phosphinate, and/or carboxylatemoieties other than an acetate moiety bonded to a Group III atom; agroup III metal oxide; a Group III alkoxy or aryloxy; or a Group IIIatom substituted with three unsaturated groups. Thus, the secondprecursor can be, e.g., indium phosphonate, indium carboxylate, indiumtristearate, indium oxide, gallium oxide, indium phenoxy, triallylindium, trivinyl indium, tributadiene indium, trialkylethynyl indium,trialkylethenyl indium, tri-4-phenylethynyl indium,trialkylphenylethynyl indium, tris-alpha-cyclohexanone indium (III), anindium tris-Cp compound, an indium tris-(substituted Cp) compound,tris-cyclopentadienyl indium(III) or tris(n-hexyl cyclopentadienyl)indium(III). The composition optionally includes a first precursor, afirst surfactant, a second surfactant, and/or a non-coordinatingsolvent. Essentially all of the features noted above apply to thisembodiment as well, as relevant; e.g., for types and composition ofnanostructures, first precursors, first and second surfactants,solvents, sacrificial oxide acceptors, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a possible sigma bond metathesis mechanism for thereaction of tribenzylphosphine with InCl₃. FIG. 1B depicts a possiblepseudo SN2 mechanism for the same reaction. FIG. 1C depicts atribenzylphosphine substituted with an electron withdrawing group. FIG.1D schematically illustrates reaction of a Group V tricarboxamide,N,N,N,N,N,N-hexaethylphosphine tricarboxamide, with an example Group IIIprecursor (an indium halide, indium phosphonate, indium carboxylate, orthe like) to form InP nanocrystals. FIG. 1E schematically illustratesreaction of a first precursor comprising a Group V atom substituted withthree carboxylate moieties with a second precursor comprising a GroupIII atom substituted with three carboxylate moieties. FIG. 1Fschematically illustrates an example reaction for synthesis of a firstprecursor comprising a Group V atom substituted with three carboxylatemoieties. FIG. 1G schematically illustrates an example reaction forsynthesis of a second precursor comprising a Group III atom substitutedwith three carboxylate moieties.

FIG. 2A schematically depicts the reaction of a triacylphosphine withtris-alpha-cyclohexanone indium (III) to produce InP nanocrystals and anester co-product. FIG. 2B illustrates a possible mechanism for thereaction of FIG. 2A. FIG. 2C outlines synthesis of a compound related totris-alpha-cyclohexanone indium (III). FIG. 2D outlines a suggestedsynthesis for tris-alpha-cyclohexanone indium (III). FIG. 2Eschematically depicts the reaction of a triacylphosphine with indiumphenoxy to produce InP nanocrystals and an ester co-product. FIG. 2Fschematically depicts the reaction of a triacylphosphine withtris-cyclopentadienyl indium (III) to produce InP nanocrystals and aketone co-product.

FIG. 3A schematically illustrates an equilibrium between first precursorTOP and second precursor InCl₃ and products chlorooctane and InP.Removal of the chlorooctane by-product, e.g., as a vapor, drives theequilibrium to the right, resulting in formation of more InPnanocrystals. FIG. 3B schematically illustrates a proposed mechanism forthe reaction, which can be carried out in the presence of one or moresuitable surfactants (e.g., TOPO).

FIGS. 4A-4C schematically depicts synthesis of example precursors. FIG.4A illustrates synthesis of tris-cyclopentadienyl indium. FIG. 4Billustrates synthesis of tris-hexylcyclopentadienyl indium. FIG. 4Cillustrates synthesis of P(COC₆H₄(CH₂)₆CH₃)₃.

FIG. 5A and FIG. 5B schematically illustrate formation of an In—Pcomplex. FIG. 5C schematically illustrates synthesis of InP nanocrystalsand a ketone co-product from the preformed precursor complex. FIG. 5Dpresents the reaction temperature profile for the synthesis. FIG. 5E2presents results of mass spec analysis, and FIG. 5E1 shows a peakcorresponding to the formula weight (fwt) 268.4 ketone co-product. FIG.5F shows a micrograph of the resulting InP nanocrystals. FIG. 5Gpresents results of XRD analysis of the resulting InP nanocrystals.

FIG. 6A schematically illustrates formation of an In—P complex. FIG. 6Bpresents the reaction temperature profile for a nanocrystal synthesisreaction. The reaction pot contains 0.4 mmol of PPh₃, 0.4 mmol ofstearic acid, and 7.0 mL of HDB (hexadecylbenzene). FIG. 6C and FIG. 6Dshow micrographs of the resulting InP nanocrystals. FIG. 6E presentsresults of XRD analysis of the resulting InP nanocrystals. FIG. 6F showsa UV-visible absorption spectrum of the resulting InP nanocrystals.

FIG. 7A presents the reaction temperature profile for a nanocrystalsynthesis reaction. FIG. 7B shows dynamic light scattering dataindicating the size of the resulting nanostructures. FIG. 7C shows aUV-visible absorption spectrum of the resulting InP nanocrystals. FIG.7D1 and FIG. 7D2 show transmission electron micrographs of the resultingtetrahedral nanocrystals. FIG. 7E presents results of XRD analysis ofthe resulting InP nanocrystals. FIG. 7F presents the reactiontemperature profile (temperature vs. time) for a nanocrystal synthesisreaction. FIG. 7G shows a UV-visible absorption spectrum of theresulting InP nanocrystals. FIG. 7H1 and FIG. 7H2 show transmissionelectron micrographs of the resulting tetrahedral nanocrystals. FIG. 7Ipresents results of XRD analysis of the resulting InP nanocrystals.

FIG. 8A and FIG. 8B schematically depict triphenylphosphine acting as anoxide acceptor in a nanostructure synthesis reaction. FIG. 8C presents aMALDI TOF mass spec background scan showing matrix peaks. FIG. 8D andFIG. 8E presents results of mass spec analysis of reaction mixtures,indicating the presence of triphenylphosphine oxide.

FIG. 9A shows a UV-visible absorption spectrum of InP nanocrystals. FIG.9B presents results of XRD analysis of the nanocrystals.

DEFINITIONS

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention pertains. The following definitionssupplement those in the art and are directed to the current applicationand are not to be imputed to any related or unrelated case, e.g., to anycommonly owned patent or application. Although any methods and materialssimilar or equivalent to those described herein can be used in thepractice for testing of the present invention, the preferred materialsand methods are described herein. Accordingly, the terminology usedherein is for the purpose of describing particular embodiments only, andis not intended to be limiting.

As used in this specification and the appended claims, the singularforms “a,” “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “ananostructure” includes a plurality of such nanostructures, and thelike.

The term “about” as used herein indicates the value of a given quantityvaries by +/−10% of the value, or optionally +/−5% of the value, or insome embodiments, by +/−1% of the value so described.

An “acyl group” has the formula RC(O)—, where R is an organic group. Theacyl group can be, e.g., substituted or unsubstituted. In a “substitutedacyl group”, at least one hydrogen in the organic group is replaced withone or more other atoms.

An “alkenyl group” refers to a linear, branched, or cyclic unsaturatedhydrocarbon moiety that comprises one or more carbon-carbon doublebonds. Alkenyl groups can be substituted or unsubstituted.

An “alkynyl group” refers to a linear, branched, or cyclic unsaturatedhydrocarbon moiety that comprises one or more carbon-carbon triplebonds. Alkynyl groups can be substituted or unsubstituted.

An “alkyl amine” is an amine having at least one alkyl substituent onthe nitrogen atom. A “monoalkyl amine” contains one alkyl group on thenitrogen, a “bialkyl amine” contains two alkyl groups on the nitrogen,and a “trialkyl amine” contains three alkyl groups on the nitrogen.

The term “alkyl-aryl group” refers to a group that comprises alkyl andaryl moieties.

The term “aryl group” refers to a chemical substituent comprising orconsisting of an aromatic group. Exemplary aryl groups include, e.g.,phenyl groups, benzyl groups, tolyl groups, xylyl groups, alkyl-arylgroups, or the like. Aryl groups optionally include multiple aromaticrings (e.g., diphenyl groups, etc.). The aryl group can be, e.g.,substituted or unsubstituted. In a “substituted aryl group”, at leastone hydrogen is replaced with one or more other atoms.

An “aspect ratio” is the length of a first axis of a nanostructuredivided by the average of the lengths of the second and third axes ofthe nanostructure, where the second and third axes are the two axeswhose lengths are most nearly equal each other. For example, the aspectratio for a perfect rod would be the length of its long axis divided bythe diameter of a cross-section perpendicular to (normal to) the longaxis.

A “branched nanostructure” is a nanostructure having three or more arms,where each arm has the characteristics of a nanorod, or a nanostructurehaving two or more arms, each arm having the characteristics of ananorod and emanating from a central region that has a crystal structuredistinct from that of the arms. Examples include, but are not limitedto, bipods, tripods, and nanotetrapods (tetrapods).

Two atoms are “bonded to” each other when they share a chemical bond,e.g., a covalent bond, a polar covalent bond, or an ionic bond.

A “by-product” or “co-product” of a nanostructure synthesis reaction isa product produced in addition to the desired nanostructure.

A “carboxamide group” has the formula —C(O)NRR′, where R and R′ areindependently selected organic groups (e.g., an alkyl or aryl group).

“Cp” represents cyclopentadiene or an unsubstituted cyclopentadienylgroup, as will be clear from the context. A cyclopentadienyl group canbe, e.g., substituted or unsubstituted. In a “substitutedcyclopentadienyl group”, at least one hydrogen is replaced with one ormore other atoms.

The terms “crystalline” or “substantially crystalline,” when used withrespect to nanostructures, refer to the fact that the nanostructurestypically exhibit long-range ordering across one or more dimensions ofthe structure. It will be understood by one of skill in the art that theterm “long range ordering” will depend on the absolute size of thespecific nanostructures, as ordering for a single crystal cannot extendbeyond the boundaries of the crystal. In this case, “long-rangeordering” will mean substantial order across at least the majority ofthe dimension of the nanostructure. In some instances, a nanostructurecan bear an oxide or other coating, or can be comprised of a core and atleast one shell. In such instances it will be appreciated that theoxide, shell(s), or other coating need not exhibit such ordering (e.g.it can be amorphous, polycrystalline, or otherwise). In such instances,the phrase “crystalline,” “substantially crystalline,” “substantiallymonocrystalline,” or “monocrystalline” refers to the central core of thenanostructure (excluding the coating layers or shells). The terms“crystalline” or “substantially crystalline” as used herein are intendedto also encompass structures comprising various defects, stackingfaults, atomic substitutions, and the like, as long as the structureexhibits substantial long range ordering (e.g., order over at leastabout 80% of the length of at least one axis of the nanostructure or itscore). In addition, it will be appreciated that the interface between acore and the outside of a nanostructure or between a core and anadjacent shell or between a shell and a second adjacent shell maycontain non-crystalline regions and may even be amorphous. This does notprevent the nanostructure from being crystalline or substantiallycrystalline as defined herein.

The “diameter of a nanocrystal” refers to the diameter of across-section normal to a first axis of the nanocrystal, where the firstaxis has the greatest difference in length with respect to the secondand third axes (the second and third axes are the two axes whose lengthsmost nearly equal each other). The first axis is not necessarily thelongest axis of the nanocrystal; e.g., for a disk-shaped nanocrystal,the cross-section would be a substantially circular cross-section normalto the short longitudinal axis of the disk. Where the cross-section isnot circular, the diameter is the average of the major and minor axes ofthat cross-section.

The “diameter of a nanorod” refers to the diameter of a cross-sectionnormal to the major principle axis (the long axis) of the nanorod. Wherethe cross-section is not circular, the diameter is the average of themajor and minor axes of that cross-section.

An “ester” has the formula RC(O)OR′, where R and R′ are independentlyselected organic groups (e.g., an alkyl or aryl group).

An “ether” comprises two carbon atoms attached to a single oxygen atom.

A “furyl group” comprises a furan ring.

A “furfuryl group” is an acyl group comprising a furan ring (e.g.,furan-2-carboxaldehyde).

A “ketone” comprises two carbon atoms attached to a single carbonylgroup.

A “Group III atom” is an atom selected from Group III of the periodictable of the elements. Examples include, but are not limited to, B, Al,Ga, In, and Tl.

A “Group V atom” is an atom selected from Group V of the periodic tableof the elements. Examples include, but are not limited to, N, P, As, Sb,and Bi.

A “Group III inorganic compound” contains a Group III atom that isdirectly bonded to at least one non-carbon atom and that is not directlybonded to a carbon atom. For example, the Group III atom can be bondedto at least one oxygen or halogen atom.

A “Group III alkoxy” contains a Group III atom directly bonded to theoxygen atom of at least one alkoxy group (which contains an alkyl groupbonded to the oxygen).

A “Group III aryloxy” contains a Group III atom directly bonded to theoxygen atom of at least one aryloxy group (which contains an aryl groupbonded to the oxygen).

A “Group III organometallic compound” contains a Group III atom directlybonded to at least one carbon atom.

A “Group V organometallic compound” contains a Group V atom directlybonded to at least one carbon atom.

The term “Group III-V semiconductor” refers to a semiconductorcontaining at least one Group III atom and at least one Group V atom.Typically, a Group III-V semiconductor includes one Group III atom andone Group V atom; examples include, but are not limited to, InN, InP,InAs, InSb, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, or AlSb.

A “heteroatom” refers to any atom which is not a carbon or hydrogenatom. Examples include, but are not limited to, oxygen, nitrogen,sulfur, phosphorus, and boron.

The term “monocrystalline” when used with respect to a nanostructureindicates that the nanostructure is substantially crystalline andcomprises substantially a single crystal. When used with respect to ananostructure heterostructure comprising a core and one or more shells,“monocrystalline” indicates that the core is substantially crystallineand comprises substantially a single crystal.

A “nanocrystal” is a nanostructure that is substantiallymonocrystalline. A nanocrystal thus has at least one region orcharacteristic dimension with a dimension of less than about 500 nm,e.g., less than about 200 nm, less than about 100 nm, less than about 50nm, or even less than about 20 nm. The term “nanocrystal” is intended toencompass substantially monocrystalline nanostructures comprisingvarious defects, stacking faults, atomic substitutions, and the like, aswell as substantially monocrystalline nanostructures without suchdefects, faults, or substitutions. In the case of nanocrystalheterostructures comprising a core and one or more shells, the core ofthe nanocrystal is typically substantially monocrystalline, but theshell(s) need not be. In one aspect, each of the three dimensions of thenanocrystal has a dimension of less than about 500 nm, e.g., less thanabout 200 nm, less than about 100 nm, less than about 50 nm, or evenless than about 20 nm. Examples of nanocrystals include, but are notlimited to, substantially spherical nanocrystals, branched nanocrystals,and substantially monocrystalline nanowires, nanorods, nanodots, quantumdots, nanotetrapods, tripods, bipods, and branched tetrapods (e.g.,inorganic dendrimers).

A “substantially spherical nanocrystal” is a nanocrystal with an aspectratio between about 0.8 and about 1.2.

A “nanorod” is a nanostructure that has one principle axis that islonger than the other two principle axes. Consequently, the nanorod hasan aspect ratio greater than one. Nanorods of this invention typicallyhave an aspect ratio between about 1.5 and about 10, but can have anaspect ratio greater than about 10, greater than about 20, greater thanabout 50, or greater than about 100, or even greater than about 10,000.Longer nanorods (e.g., those with an aspect ratio greater than about 10)are sometimes referred to as nanowires. The diameter of a nanorod istypically less than about 500 nm, preferably less than about 200 nm,more preferably less than about 150 nm, and most preferably less thanabout 100 nm, about 50 nm, or about 25 nm, or even less than about 10 nmor about 5 nm. Nanorods can have a variable diameter or can have asubstantially uniform diameter, that is, a diameter that shows avariance less than about 20% (e.g., less than about 10%, less than about5%, or less than about 1%) over the region of greatest variability.Nanorods are typically substantially crystalline and/or substantiallymonocrystalline, but can be, e.g., polycrystalline or amorphous.

A “nanostructure” is a structure having at least one region orcharacteristic dimension with a dimension of less than about 500 nm,e.g., less than about 200 nm, less than about 100 nm, less than about 50nm, or even less than about 20 nm. Typically, the region orcharacteristic dimension will be along the smallest axis of thestructure. Examples of such structures include nanowires, nanorods,nanotubes, branched nanostructures, nanotetrapods, tripods, bipods,nanocrystals, nanodots, quantum dots, nanoparticles, and the like.Nanostructures can be, e.g., substantially crystalline, substantiallymonocrystalline, polycrystalline, amorphous, or a combination thereof.In one aspect, each of the three dimensions of the nanostructure has adimension of less than about 500 nm, e.g., less than about 200 nm, lessthan about 100 nm, less than about 50 nm, or even less than about 20 nm.

A “nanotetrapod” is a generally tetrahedral branched nanostructurehaving four arms emanating from a central region or core, where theangle between any two arms is approximately 109.5 degrees. Typically,the core has one crystal structure and the arms have another crystalstructure.

A “phosphine” has the formula PRR′R″, where R, R′, and R″ areindependently an alkyl group, acyl group, aryl group (e.g., alkylarylgroup), alkenyl group, alkynyl group, ester group, hydrogen, halide, orthe like.

A “tri-n-alkyl phosphine” has the formula PR₃, where R is an n-alkylgroup.

A “phosphinic acid” has the formula RR′P(O)OH, where R and R′ areindependently any organic group (e.g., any alkyl or aryl group) orhydrogen. A “phosphinate moiety” thus has the formula RR′P(O)O—.

A “phosphonic acid” has the formula RP(O)(OH)₂ or RP(O)(OR′)(OH), whereR and R′ are independently an organic group (e.g., an alkyl or arylgroup). A “phosphonate moiety” thus has the formula RP(O)(OH)O— orRP(O)(OR′)O—.

A “carboxylic acid” has the formula RC(O)OH, where R is an organic group(e.g., an alkyl group or an aryl group). A “carboxylate moiety” thus hasthe formula RC(O)O—.

A “boronic acid” has the formula RB(OH)₂, where R is an organic group(e.g., an alkyl or aryl group) or hydrogen.

A “sulfonic acid” has the formula RS(O)₂OH, where R is an organic group(e.g., an alkyl or aryl group) or hydrogen.

A “precursor” in a nanostructure synthesis reaction is a chemicalsubstance (e.g., a compound or element) that reacts, e.g., with anotherprecursor, and thereby contributes at least one atom to thenanostructure produced by the reaction.

A “surfactant” is a molecule capable of interacting (whether weakly orstrongly) with one or more faces of a nanostructure and/or with one ormore precursors used in producing the nanostructure.

A “non-coordinating solvent” is one that does not interact with one ormore faces of a nanostructure and/or with one or more precursors used inproducing the nanostructure. A typical weakly binding surfactantcomprises a heteroatom having a free (non-bonded within the surfactant)pair of electrons, while a typical non-coordinating solvent does notinclude such a heteroatom and free pair of electrons.

A “trisubstituted Group V atom” is a Group V atom that is directlybonded to three other atoms. The three other atoms can be identical ordistinct. Each of the three other atoms is optionally part of a chemicalgroup.

A “triacyl substituted Group V atom” is a Group V atom that is bonded tothree identical acyl groups. The acyl group can be, e.g., substituted orunsubstituted.

A “trialkyl substituted Group V atom” is a Group V atom that is bondedto three identical alkyl groups. The alkyl group can be, e.g.,unbranched or branched and/or substituted or unsubstituted.

A “triaryl substituted Group V atom” is a Group V atom that is bonded tothree identical aryl groups. The aryl group can be, e.g., substituted orunsubstituted.

An “alkyl group” refers to a linear, branched, or cyclic saturatedhydrocarbon moiety and includes all positional isomers. Alkyl groups canbe, e.g., substituted or unsubstituted.

An “unbranched alkyl group” is a linear, n-alkyl group.

An “unsubstituted alkyl group” has the formula —(CH₂)—CH₃, where n isgreater than or equal to zero. In a “substituted alkyl group”, at leastone hydrogen is replaced with one or more other atoms. For example, atleast one hydrogen can be replaced with a moiety containing one or morecarbon, oxygen, sulfur, nitrogen, or halogen atoms. An alkyl group can,e.g., be branched or unbranched.

An “unsaturated group” contains at least one element of unsaturation. An“element of unsaturation” is a double bond (of any type), a triple bond(of any type), or a ring.

A variety of additional terms are defined or otherwise characterizedherein.

DETAILED DESCRIPTION

Methods for colloidal synthesis of Group II-VI semiconductornanostructures are known in the art. Such methods include techniques forcontrolling nanostructure growth, e.g., to control the size and/or shapedistribution of the resulting nanostructures. For example, methods forcolloidal synthesis of Group II-VI substantially spherical nanocrystals,nanorods, and nanotetrapods have been described. See, e.g., Manna et al.(2002) “Shape control of colloidal semiconductor nanocrystals” Journalof Cluster Science 13:521-532; Peng et al. (2000) “Shape control of CdSenanocrystals” Nature 404:59-61; Puntes et al. (2001) “Colloidalnanocrystal shape and size control: The case of cobalt” Science291:2115-2117; U.S. Pat. No. 6,225,198 to Alivisatos et al., entitled“Process for forming shaped group II-VI semiconductor nanocrystals, andproduct formed using process”; Alivisatos (1996) “Semiconductorclusters, nanocrystals, and quantum dots” Science 271:933-937; Peng etal. (1997) “Epitaxial growth of highly luminescent CdSe/CdS core/shellnanocrystals with photostability and electronic accessibility” J. Am.Chem. Soc. 119:7019-7029; Murray et al. (1993) “Synthesis andcharacterization of nearly monodisperse CdE (E=sulfur, selenium,tellurium) semiconductor nanocrystallites” J. Am. Chem. Soc. 115:8706-8715; and WO 03/054953 by Alivisatos et al., entitled “Shapednanocrystal particles and methods for making the same”.

In brief, Group II-VI semiconductor nanostructures can be produced byrapidly injecting precursors that undergo pyrolysis into a hotsurfactant. The precursors can be injected simultaneously orsequentially. The precursors rapidly react to form nuclei. Nanostructuregrowth occurs through monomer addition to the nuclei, typically at agrowth temperature that is lower than the injection/nucleationtemperature.

The surfactant molecules interact with the surface of the nanostructure.At the growth temperature, the surfactant molecules rapidly adsorb anddesorb from the nanostructure surface, permitting the addition and/orremoval of atoms from the nanostructure while suppressing aggregation ofthe growing nanostructures. In general, a surfactant that coordinatesweakly to the nanostructure surface permits rapid growth of thenanostructure, while a surfactant that binds more strongly to thenanostructure surface results in slower nanostructure growth. Thesurfactant can also interact with one (or more) of the precursors toslow nanostructure growth.

Nanostructure growth in the presence of a single surfactant typicallyresults in spherical nanostructures. Using a mixture of two or moresurfactants, however, permits growth to be controlled such thatnon-spherical nanostructures can be produced, if, for example, the two(or more) surfactants adsorb differently to different crystallographicfaces of the growing nanostructure. For example, substantially sphericalCdSe nanocrystals can be grown in trioctyl phosphine oxide (TOPO), whileCdSe nanorods can be grown in a mixture of TOPO and hexyl phosphonicacid (Peng et al., supra).

A number of parameters are thus known to affect nanostructure growth andcan be manipulated, independently or in combination, to control the sizeand/or shape distribution of the resulting nanostructures. Theseinclude, e.g., temperature (nucleation and/or growth), precursorcomposition, time-dependent precursor concentration, ratio of theprecursors to each other, number of surfactants, surfactant composition,and ratio of surfactant(s) to each other and/or to the precursors.

Growth of a few types of Group III-V semiconductor nanostructures hasalso been described (see, e.g., U.S. Pat. No. 6,306,736 by Alivisatos etal. entitled “Process for forming shaped group III-V semiconductornanocrystals, and product formed using process”). For example, Wells etal. (1989) “The use of tris(trimethylsilyl)arsine to prepare galliumarsenide and indium arsenide” Chem. Mater. 1:4-6, Guzelian et al. (1996)“Colloidal chemical synthesis and characterization of InAs nanocrystalquantum dots” 69: 1432-1434, Guzelian et al. (1996) “Synthesis ofsize-selected, surface-passivated InP nanocrystals” J. Phys. Chem.100:7212-7219, and U.S. Pat. No. 5,505,928 to Alivisatos et al. entitled“Preparation of III-V semiconductor nanocrystals” describe the synthesisof substantially spherical group III-V nanocrystals or quantum dots.Published US Patent Application No. 2003/0214699 by Banin et al.entitled “Method for producing inorganic semiconductor nanocrystallinerods and their use” describes the use of a metal catalyst to nucleatethe growth of rod-shaped Group III-V nanocrystals. The resultingnanocrystals, however, contain non-semiconducting material at one end,which can undesirably affect the electrical properties of thenanocrystals.

Thus, although growth of Group II-VI semiconductor nanostructuressuggests principles that can be applied to growth of Group III-Vnanostructures, application of these principles to produce Group III-Vnanostructures of desired shapes and/or sizes has not beenstraightforward, in part due to lack of suitable precursors,surfactants, and combinations thereof. For example, eithertris(trimethylsilyl)arsine or tris(trimethylsilyl)phosphine is typicallyused as the Group V atom source in synthesis of Group III-Vnanostructures. Phosphonic acids, which are typically used assurfactants to control the growth of Group II-VI nanostructures toproduce nanorods or nanotetrapods, react with the tris(trimethylsilyl)precursors, and can thus not be used in combination with theseprecursors to control synthesis of Group III-V nanostructures withoutthe potential for non-beneficial side reactions to take place.

In one aspect, the present invention overcomes the above noteddifficulties (e.g., the lack of suitable precursors andprecursor-surfactant combinations for synthesis of Group III-Vnanostructures) by providing novel Group III and Group V precursors. Anumber of methods for producing Group III-V nanostructures aredescribed, along with related compositions. For example, use ofprecursors including trimethyl- and triethyl-substituted Group V atomsare described; these precursors do not react with phosphonic acids,which can thus be used as surfactants to control the shape of theresulting nanostructures. Methods and compositions for producing GroupIII inorganic compounds that can be used as precursors for nanostructuresynthesis are provided. Suitable surfactants are also described (e.g.,long chain tri-n-alkyl phosphines capable of withstanding highertemperatures, and unsaturated Group V derivatives), as are methods forincreasing the yield of nanostructures from a synthesis reaction.Methods for producing nanostructures at high temperatures and/or inconjunction with a stable co-product are also features of the invention,as are compositions related to the methods.

Group V Precursors

In one aspect, the invention relates to novel Group V precursors (e.g.,precursors that include a Group V atom substituted with threeunsaturated groups). Methods using such precursors in production ofGroup III-V semiconductor nanostructures are provided. Related methodsusing Group V precursors at high temperatures are described.Compositions related to the methods are also provided.

Methods

Thus, a first general class of embodiments provides methods forproduction of Group III-V semiconductor nanostructures. In the methods,a first precursor and a second precursor are provided, and the first andsecond precursors are reacted to produce the nanostructures. The firstprecursor comprises a trisubstituted Group V atom. The trisubstitutedGroup V atom is other than a) a trialkyl substituted Group V atomcomprising an unbranched and unsubstituted alkyl group, b) an H₃substituted Group V atom, c) an H₂alkyl substituted Group V atomcomprising an unbranched and unsubstituted alkyl group, d) an Halkyl₂substituted Group V atom comprising an unbranched and unsubstitutedalkyl group, or e) a tris(trialkylsilyl) substituted Group V atom. Incertain embodiments, first precursors of the invention optionallyexclude any trialkyl substituted, H₂alkyl substituted, or Halkyl₂substituted Group V atom. The second precursor comprises a Group IIIatom.

The Group V atom can be any atom selected from Group V of the periodictable of the elements. In a preferred class of embodiments, the Group Vatom is N, P, As, Sb, or Bi.

The three substituents on the Group V atom in the first precursor can beidentical or distinct. The three substituents can be independently anyorganic group or hydrogen, for example. In one class of embodiments, thefirst precursor is a Group V organometallic compound, e.g., which can beused in a low temperature route or in a high temperature precursordecomposition route to solution-based synthesis of Group III-Vsemiconductor nanostructures.

In one aspect, the first precursor comprises a Group V atom substitutedwith three unsaturated groups (e.g., any group including at least onedouble or triple bond or ring, including, but not limited to, alkenyl,alkynyl, acyl, and aryl groups). For example, the first precursor can betriallylphosphine, trivinylphosphine, tributadienylphosphine,trialkylethynylphosphine, trialkylethenylphosphine,tri(4-phenylethynyl)phosphine, or trialkylphenylethynylphosphine. See,e.g., Beletskaya et al. (2003) Organic Letters 5:4309-4311 for adescription of ethynylphosphine synthesis and example ethynylphosphines.As another example, the first precursor can include a Group V atomsubstituted with three furyl or furfuryl groups; e.g., the firstprecursor can be tri-2-furylphosphine or tri-2-furfurylphosphine. See,e.g., Farina and Krishnan (1991) J. Am. Chem. Soc. 113:9585-9595.

In one class of embodiments, the first precursor comprises a triacylsubstituted Group V atom. The acyl group can be, e.g., unsubstituted orsubstituted. For example, the first precursor can be a triacylphosphineor a triacylarsine, e.g., tribenzoylphosphine, trialkylbenzoylphosphine,trihexylbenzoylphosphine, trialkoylphosphine, or trihexoylphosphine.Synthesis of acyl phosphines has been described, e.g., in Tyka et al.(1961) Roczniki Chem. 35:183, Tyka et al. (1962) Ref. Zh. Khim. 1 Zh245, Barycki et al. (1978) Tetrahedron Letters 10:857, and Kost (1979)Tetrahedron Letters 22:1983.

In a related class of embodiments, the first precursor comprises atriaryl substituted Group V atom. The aryl group can be, e.g.,unsubstituted or substituted. The substituent optionally comprises anelectron donating group or an electron withdrawing group (a wide varietyof electron donating and withdrawing groups are known in the art and canbe adapted for use in the present invention). In one class of exampleembodiments, the first precursor comprises a tribenzyl substituted GroupV atom; for example, the first precursor can be tribenzylphosphine ortribenzylarsine

Although the scope of the present invention is not intended to belimited to any particular mechanism, FIG. 1A and FIG. 1B compare twopossible mechanisms for reaction of a tribenzylphospine first precursorwith an InCl₃ second precursor (sigma bond metathesis in FIG. 1A andpseudo SN2 in FIG. 1B). FIG. 1C depicts an example tribenzylphospinesubstituted with an electron withdrawing group (EWG), e.g., F or CF₃;the presence of such an electron withdrawing substituent can, e.g.,accelerate the reaction illustrated in FIG. 1A.

In another related class of embodiments, the first precursor comprises aGroup V atom substituted with three carboxamide groups. Thus, forexample, the first precursor can be a tricarboxamide phosphine, e.g.,N,N,N,N,N,N-hexaethylphosphine tricarboxamide. Without limitation to anyparticular mechanism, reaction of N,N,N,N,N,N-hexaethylphosphinetricarboxamide with an indium halide, indium phosphonate, indiumcarboxylate, or the like to form InP nanocrystals is schematicallyillustrated in FIG. 1D.

In another class of embodiments, the first precursor comprises atrialkyl substituted Group V atom comprising a substituted and/orbranched alkyl group. For example, the first precursor can include atri-t-butyl substituted Group V atom; e.g., the first precursor can betri-t-butylphosphine.

It is worth noting that WO 03/054953 by Alivisatos et al. suggests theuse of precursors including a tri-alkyl substituted Group V atom;however, only n-alkyl substituents are described. Precursors withbranched and/or substituted alkyl substituents on the Group V atom canunexpectedly work considerably better in nanostructure synthesisreactions, since they can react more quickly and/or form more stableby-products than do tri-n-alkyl substituted Group V atoms (e.g.,tri-n-alkyl phosphines or arsines). Similarly, precursors with arylsubstituents on the Group V atom (e.g., tribenzylphosphine) can alsoreact more quickly and/or form more stable by-products than dotri-n-alkyl substituted Group V atoms (e.g., tri-n-alkyl phosphines).

In certain embodiments, the first precursor is a Group V inorganiccompound. For example, in one class of embodiments, the first precursorcomprises a Group V atom substituted with three carboxylate moieties orwith three phosphinate moieties. In one embodiment, the Group V atom isP such that the first precursor is a phosphite ester.

The first precursor can be used in combination with essentially anysuitable second precursor, whether previously known in the art ordescribed herein. The Group III atom can be any atom selected from GroupIII of the periodic table of the elements. In a preferred class ofembodiments, the Group III atom is B, Al, Ga, In, or Tl.

In one class of embodiments, the second precursor is a Group IIIinorganic compound (e.g., a Group III halide, or a compound in which theGroup III atom is directly bonded to at least one oxygen atom or otherheteroatom, e.g., nitrogen).

In one class of embodiments, the second precursor is a Group III halide(sometimes also referred to as a Group III halide compound). Thus, inthis class of embodiments, the second precursor is YZ₃, where Y is aGroup III atom (e.g., B, Al, Ga, In, or Tl) and Z is a halogen atom(e.g., F, Cl, Br, I, or At).

In another class of embodiments, the second precursor comprises one ormore phosphonate, phosphinate, carboxylate, sulfonate, and/or boronatemoieties bonded to the Group III atom. For example, the second precursorcan comprise a bi- or tri-substituted Group III atom (e.g., atricarboxylate, bi- or tri-phosphonate, or triphosphinate substitutedGroup III atom). Thus, in one class of embodiments, the second precursoris Y(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, or Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. The alkyl or aryl group can be, e.g., substituted orunsubstituted. For example, the second precursor can be an indiumphosphonate or indium carboxylate (e.g., indium triacetate or indiumtristearate).

In yet another class of embodiments, the second precursor is a Group IIImetal oxide. For example, the second precursor can be indium oxide orgallium oxide. As another example, the second precursor can be a GroupIII alkoxy or Group III aryloxy (e.g., a Group III phenoxy, e.g., indiumphenoxy). Reaction of indium phenoxy as the second precursor with atriacylphosphine first precursor to eliminate an ester co-product andform InP nanocrystals is depicted in FIG. 2E. Synthesis of Group IIIalkoxys, e.g., indium alkoxys, has been described. For example, generalindium alkoxys have been described in Bradley et al. (1990) Polyhedron9(5):719-726; Bradley et al. (1988) J. Chem. Soc. Chem. Comm.(18):1258-1259; and Chatterje et al. (1976) Journal of the IndianChemical Society 53(9):867, while alkoxyIndium with electron withdrawinggroups is described in Miinea et al. (1999) Inorg. Chem. 38:4447.

In one class of embodiments, instead of being a Group III inorganiccompound, the second precursor is a Group III organometallic compound.In some embodiments, the second precursor comprises a tri-substitutedGroup III atom in which the three substituents are independently anyorganic group or hydrogen. For example, the second precursor can be analkyl metal or a trialkyl metal, e.g., trimethyl indium or triethylindium. In one aspect, the second precursor comprises a Group III atomsubstituted with three unsaturated groups (e.g., any group including atleast one double or triple bond or ring, including, but not limited to,alkenyl, alkynyl, acyl, and aryl groups). For example, the secondprecursor can be triallyl indium, trivinyl indium, tributadiene indium,trialkylethynyl indium, trialkylethenyl indium, tri-4-phenylethynylindium, or trialkylphenylethynyl indium. In other embodiments, thesecond precursor comprises a Group III atom substituted with threecyclic ketone groups; for example, the second precursor can betris-alpha-cyclohexanone indium (III). In yet other embodiments, thesecond precursor comprises a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups. For example,the second precursor can be an indium tris-Cp compound or an indiumtris-(substituted Cp) compound, for example, tris-cyclopentadienylindium(III) or tris(n-hexyl cyclopentadienyl) indium(III). Preparationof such tri-unsaturated Group III compounds is known in the art; see,e.g., Schiefer et. al. (2003) Inorg. Chem. 42:4970 for a description ofpreparation of Group III tris-(ethynyl)indium compounds.

Reaction of tris-alpha-cyclohexanone indium (III) as the secondprecursor with a triacylphosphine first precursor to form an ester andInP nanocrystals is illustrated in FIG. 2A. Without intending to belimited by any particular mechanism, the key step is the dative bondbetween indium and phosphorous, an interaction that forms a precursor tothe nanocrystal. With this interaction, electron donation fromphosphorous to indium will make the indium electron rich and shouldpromote bond breaking of indium-carbon bonds to the ligands, especiallyif the anion formed as the result of the reaction is relatively stable.That anion should attack electrophiles, intra or intermolecularly,especially one held in immediate proximity, such as a carbonyl carbon.Therefore a possible elimination mechanism could be the one shown inFIG. 2B that results in the formation of an ester. Overall, it isformation of an enol by breakage of the indium-carbon bond followed byattack by oxygen on the electrophilic carbon of the acyl phosphine, asshown in FIG. 2B. The enol is stabilized by two significant resonanceforms with negative charge on carbon or on oxygen. Synthesis ofmolecules similar to tris-alpha-cyclohexanone indium (III) has beendescribed, e.g., in Lehmann et al. Org. Lett. 5(14):2405, Boeckman etal. (1977) Tetrahedron Lett. 18:4187, and Boeckman et al. (1981)Tetrahedron 37:3997 (tris-(dihydropyranyl)In(III) synthesis) and isillustrated in FIG. 2C. Tris-alpha-cyclohexanone indium (III) can besynthesized through a similar process, as illustrated in FIG. 2D, forexample. See also Lehmann et al. (2003) Org. Lett. 5:2405 for synthesisof an organometallic In compound with cyclic hydrocarbon ligandscontaining oxygen (In(DHP)₃).

As another example, without intending to be limited by any particularmechanism, reaction of tris-cyclopentadienyl indium(III) (InCp₃) as thesecond precursor with a triacylphosphine first precursor, e.g., byelimination of a cyclopentadieneide anion, is illustrated in FIG. 2F.Alternatively or in addition, this reaction may occur through aDiels-Alder cycloaddition between the acyl group of the phosphine andthe cyclopentadiene ring of the indium-containing second precursor,e.g., depending on reaction temperature and light (described forruthenium compounds in Ji et al. (1992) Organometallics 11:1840-1855).The synthesis of InCp₃ and substituted Cp derivatives has beendescribed, e.g., in Beachley et al. (2002) Organometallics 21:4632-4640and Beachley et al. (1990) Organometallics 9:2488.

In general, without intending to be limited by any particular mechanism,unsaturated substituents on the P or other Group V element can result incycloadditions, thus changing the bonding character between the GroupIII and Group V atoms. Group V precursors that contain unsaturatedmoieties bonded to the Group V atom can promote pi-backbonding from thelate metal indium or other Group III atom to the Group V atom, thusstrengthening the III-V interaction and weakening bonds to the moietiesattached to the Group III and V atoms. This can result in enhancedcleavage of organometallic bonds to the indium or other Group III metalcenter.

In one class of embodiments, the first precursor comprises atrisubstituted Group V atom where the substituents are dienes, while thesecond precursor includes a trisubstituted Group III atom where thesubstituents are dienophiles. In a related class of embodiments, thefirst precursor comprises a trisubstituted Group V atom where thesubstituents are dienophiles while the second precursor includes atrisubstituted Group III atom where the substituents are dienes. Thediene and dienophile substituents can, e.g., undergo Diels-Adlerreactions. See, e.g., Yang and Chan (2000) J. Am. Chem. Soc.122:402-403, which describes a Diels-Adler reaction involving indium(I)with elimination of Cp, and Ji et al. (1992) Organometallics11:1840-1855, and examples herein.

As will be evident, the first and second precursors described herein canbe used in any of a variety of combinations. To list only a fewexamples, the first precursor can include a triacyl substituted Group Vatom while the second precursor includes a Group III atom substitutedwith three unsaturated groups; for example, the first precursor can betribenzoylphosphine and the second precursor tris-cyclopentadienylindium, the first precursor tri-heptylbenzoylphosphine and the secondprecursor tris-cyclopentadienyl indium, or the first precursortri-heptylbenzoylphosphine and the second precursortris-hexylcyclopentadienyl indium.

Another example precursor combination is illustrated in FIG. 1E. In thisexample, the first precursor comprises a Group V atom substituted withthree carboxylate moieties, and the second precursor comprises a GroupIII atom substituted with three carboxylate moieties. (In similarexamples, one or both precursors can instead include three phosphinatemoieties.) The precursors can, for example, be reacted in the presenceof a non-coordinating solvent (e.g., hexadecylbenzene), an oxygenscavenger (e.g., a pi-acid oxide acceptor such as triphenylphosphine),and/or a surfactant (e.g., an alkyl-substituted carboxylic, phosphonic,phosphinic, or sulfonic acid, or a combination thereof, which canpromote thermodynamic equilibrium and/or associate with a surface of theresulting nanocrystals, e.g., stearic acid). Example reactions forsynthesis of these first and second precursors is outlined in FIG. 1Fand FIG. 1G, respectively. Without intending to be limited to anyparticular mechanism, it is thought that III and V precursors such asthese inorganic esters can reversibly decompose into III-V nanocrystalsand that such promotion of thermodynamic equilibrium can increasequality and facilitate shape control of the resulting nanocrystals.

The first and second precursors are typically reacted in the presence ofat least one surfactant. For example, the precursors can be reacted inthe presence of a first surfactant, a second surfactant, or a mixture offirst and second surfactants.

The first surfactant is typically (but not necessarily) one thatinteracts relatively weakly with the surface of the nanostructuresand/or the precursors. Suitable first surfactants include, but are notlimited to, tri-n-alkyl phosphines (e.g., TOP and tri-n-butyl phosphine(TBP)), tri-n-alkyl phosphine oxides (e.g., TOPO), alkyl amines (e.g.,monoalkyl amines and bialkyl amines, or trialkyl amines such astrioctylamine), and alkyl- and/or aryl-thiols. Suitable firstsurfactants also include unsaturated Group V derivatives; the firstsurfactant can comprise a Group V atom substituted with threeunsaturated groups (e.g., alkenyl or alkynyl groups). Examples includetrisalkylphenylethynylphosphines, e.g.,tri(ethynylbenzene-hexyl)phosphine,tris(ethynylbenzene-pentyl)phosphine, and the other unsaturatedphosphines noted herein. As just one specific example, a trialkoylphosphine can be used as the Group III precursor andtri(ethynylbenzene-hexyl)phosphine as the first surfactant, since thetrialkoyl phosphine will react at a lower temperature than thetri(ethynylbenzene-hexyl)phosphine will.

A suitable surfactant is typically a liquid at the temperature at whichthe nanostructures are grown (and at the nucleation temperature, if itis different than the growth temperature). Additionally, the surfactantshould be stable at the growth temperature (and the nucleationtemperature, if higher). Surfactants that can withstand highertemperatures, e.g., long chain tri-n-alkyl phosphines, are thuspreferable in some embodiments. In one class of embodiments, the firstsurfactant is a C12-C30 tri-n-alkyl phosphine, e.g., tri-n-dodecylphosphine or tri-n-hexadecyl phosphine. Synthesis of such long chainalkyl phosphines is described in, e.g., Franks et al. (1979) “Thepreparation and properties of tertiary phosphines and tertiary phosphineoxides with long alkyl chains” J. Chem. Soc., Perkin 1 3029-3033.

The second surfactant, as noted, can be used whether a first surfactantis used or not; when a combination of first and second surfactants isused, the second surfactant is typically (but not necessarily) one thatadsorbs differently to different crystallographic faces of thenanostructure and/or that adsorbs differently than does the firstsurfactant. Suitable second surfactants include, but are not limited to,alkyl amines (e.g., mono-, bi-, and tri-alkyl amines; typically, thefirst surfactant is not also an alkyl amine) and phosphonic acids (e.g.,a C2-30 alkylphosphonic acid), phosphinic acids (e.g., a C2-30bialkylphosphinic acid), carboxylic acids (e.g., a C2-30 alkylcarboxylicacid), boronic acids, and sulfonic acids, as well as deprotonated formsor condensates thereof. It will be evident that not all possiblecombinations of surfactants are suitable for use; for example, mixing anamine surfactant with an acid surfactant can produce a salt (e.g., aninsoluble salt), in which case the surfactants are typically not used incombination with each other.

The first and second precursors can optionally be reacted in thepresence of at least one non-coordinating solvent (and, preferably, alsoin the presence of one or more surfactants, unless one of the precursorscan also function as a surfactant). Preferred solvents include thosewith a boiling point greater than 100° C. Suitable non-coordinatingsolvents include long chain alkanes or alkenes, alkane substituted arylderivatives, and the like. For example, hexadecane, octadecane,octadecene, phenyldodecane (also called dodecyl benzene),phenyltetradecane (also called tetradecylbenzene), or phenylhexadecane(also called hexadecylbenzene) can be used.

Thus, in one class of embodiments, the first and second precursors arereacted in the presence of a non-coordinating solvent, e.g., an alkaneor an alkene, e.g., hexadecane, octadecane, octadecene, phenyldodecane,phenyltetradecane, or phenylhexadecane.

In one class of embodiments, the first and second precursors are reactedin the presence of the non-coordinating solvent and a first and/orsecond surfactant (e.g., any of those described herein). For example,the first and second precursors can be reacted in the presence of thenon-coordinating solvent (e.g., phenylhexadecane) and a carboxylic acid(e.g., stearic acid), and optionally also in the presence of asacrificial oxide acceptor (e.g., triphenylphosphine).

It is worth noting that, in certain embodiments, the same substance canserve as both a precursor and a surfactant. For example, a trialkoylphosphine, a triaroyl phosphine, a trialkyl phosphine (e.g., TOP), orthe like, can serve as both a Group III precursor and a surfactant in ananostructure synthesis reaction. See, e.g., Example 7 herein.

Suitable reaction conditions (e.g., choice of precursors andsurfactant(s), ratio of surfactants, ratio of precursors andsurfactants, ratio of precursors to each other, concentration ofprecursors, and temperature) can be empirically determined as is knownin the art to produce the desired size and/or shape nanostructures fromthe reaction.

As briefly described above for growth of Group II-VI semiconductornanostructures, using a mixture of surfactants, varying the ratio of thesurfactant(s) to the precursors, and/or varying the ratio of theprecursors to each other permits the shape and/or size of the resultingnanostructures to be controlled.

Thus, in one class of embodiments, reacting the first and secondprecursors comprises reacting the first and second precursors in thepresence of at least a first surfactant and a second surfactant, wherebythe shape of the nanostructures produced is capable of being controlledby adjusting the ratio of the first and second surfactants. For example,the ratio of the first and second surfactants can be adjusted to producesubstantially spherical nanocrystals, nanorods, branched nanostructures,and/or nanotetrapods. For example, in certain embodiments, increasingthe ratio of the second surfactant to the first surfactant can result ingrowth of nanorods or nanotetrapods, primarily or exclusively, ratherthan spherical nanocrystals.

Additional surfactants can also be used to help control the shape of theresulting nanocrystals. Thus, in some embodiments, the first and secondprecursors are reacted in the presence of a first surfactant, a secondsurfactant, and a third surfactant (e.g., a mixture of TOPO, hexylphosphonic acid, and tetradecyl phosphonic acid). Fourth, fifth, etc.surfactants are optionally also used.

In a related class of embodiments, reacting the first and secondprecursors comprises reacting the first and second precursors in thepresence of a second surfactant, whereby the shape of the nanostructuresproduced is capable of being controlled by adjusting the ratio of thesecond surfactant and the first or second precursor. For example, theratio of the second surfactant and the first or second precursor can beadjusted to produce substantially spherical nanocrystals, nanorods,branched nanostructures, and/or nanotetrapods.

In another related class of embodiments, the ratio of the first andsecond precursors is adjusted to control the shape of the nanostructuresproduced. As for the embodiments above, the ratio of the first andsecond precursors can be adjusted to produce, e.g., substantiallyspherical nanocrystals, nanorods, branched nanostructures, and/ornanotetrapods.

Similarly, the concentrations of the first and second precursors can beadjusted to influence the shape of the nanostructures produced; forexample, by increasing or decreasing the amount of each precursorinitially provided, by introducing additional fresh first and/or secondprecursor as the reaction progresses, or the like.

It is worth noting that choice of first and second precursors can alsoaffect the shape of the nanostructures produced by influencing thekinetics of the reaction. For example, the various Group III halidesthat are optionally used as second precursors in certain embodimentsreact at different rates; e.g., InBr₃ or InI₃ can react more quicklythan InCl₃ with TOP to form InP nanostructures. Similarly, example firstprecursors tri-t-butylphosphine and tri-benzylphosphine can react morequickly than TOP and can thus increase the reaction rate. As oneexample, reactivity of the precursors can be finely regulated byelectron donating and/or withdrawing substituents on groups substitutingthe Group III and/or Group V atoms; for example, a combination of anelectron donating substituent on the acyl group of a tri-acylsubstituted Group V atom and an electron withdrawing substituent on thesubstituted Group III atom can be used to control reaction kinetics anddesired crystal growth.

Alternatively or in addition, the temperature can be controlled tocontrol the shape and/or size distribution of the resultingnanostructures. Thus, in one class of embodiments, reacting the firstand second precursors to produce the nanostructures includes heating atleast one surfactant (e.g., a first and a second surfactant) to a firsttemperature; contacting the first and second precursors and the heatedsurfactant, whereby the first and second precursors react to form nucleicapable of nucleating nanostructure growth; and maintaining the firstand second precursors, the surfactant, and the nuclei at a secondtemperature. The second temperature permits growth of the nuclei toproduce the nanostructures, whereby the first and second precursorsreact to grow the nanostructures from the nuclei. The first (nucleation)temperature is typically greater than the second temperature, e.g., byabout 40-80° C., about 20-40° C., about 10-20° C., about 5-10° C., orabout 0-5° C.; the first and second temperatures can, however, be equal,or the first temperature can be less than the second temperature (e.g.,by about 40-80° C., about 20-40° C., about 10-20° C., about 5-10° C., orabout 0-5° C.). Different first and second temperatures can be used,e.g., to control the nucleation phase and growth phase separately (forexample, a nanotetrapod can be produced by reacting precursors at alower temperature to produce the zinc blende central region of thenanotetrapod, then increasing the temperature to promote wurtzite growthand produce the arms of the nanotetrapod).

Nucleation and/or growth at high temperatures may be necessary for useof certain precursors and/or desirable for producing certainnanostructure shapes. For example, under certain conditions, highertemperatures favor nanorod and nanotetrapod growth over sphericalnanocrystal growth. Thus, in some embodiments, the first temperature isat least 300° C., at least 330° C., at least 360° C., at least 380° C.,at least 400° C., or at least 420° C. In some embodiments, the secondtemperature is at least 250° C., at least 275° C., at least 300° C., atleast 320° C., at least 340° C., at least 360° C., at least 380° C., atleast 400° C., or at least 420° C. As noted previously, long chaintri-n-alkyl phosphines, for example, are optionally used as firstsurfactants at these higher temperatures.

As will be described in greater detail below, yield of nanostructuresfrom the reaction is optionally increased by removal of one or moreby-products during the reaction. Thus, in some embodiments, the firstand second precursors react to produce the nanostructures and aby-product that has a boiling point or sublimation temperature that isless than the second temperature. The methods include removing at leasta portion of the by-product as a vapor.

As noted, the precursors can be added either simultaneously orsequentially to a reaction vessel in which nanostructure synthesis isperformed. The first and second precursors can, e.g., be injectedseparately into the reaction vessel (containing, e.g., a surfactant,solvent, and/or the like). Alternatively, the first and secondprecursors can be pre-mixed, e.g., in a suitable solvent, and permittedto form a complex (e.g., a Group III-V complex, e.g., an In—P complex,in which the In is coordinated by P), then introduced into the reactionvessel. See, e.g., Examples 7-9 herein.

Thus, in one class of embodiments, reacting the first and secondprecursors to produce the nanostructures includes contacting the firstand second precursors, which form a Group III-V complex, e.g., in whichthe Group III atom is coordinated by a Group V atom. The Group III-Vcomplex is then reacted to produce the nanostructures. The complex isoptionally isolated after it is formed, and can, e.g., be stored (e.g.,frozen) and reacted at a later time (e.g., by heating).

In one aspect, multiple precursors are used, e.g., to assist incontrolling growth of the nanostructures. For example, in one class ofembodiments, one set of precursors is used for nucleation of thenanostructures while another set of precursors is used for growth. Asjust one example, InCp₃ or In(hexylCp₃) andtris(4-alkylbenzoyl)phosphine precursors are used for nucleation at orabove room temperature, while InCp₃ andtris(4-alkylethynylbenzene)phosphine precursors are used for growth at ahigher temperature (e.g., greater than 300° C.). Thus, reacting thefirst and second precursors to produce the nanostructures optionallyincludes reacting the first and second precursors to produce nuclei,providing a third precursor comprising a Group III atom and a fourthprecursor comprising a Group V atom, and reacting the third and fourthprecursors to produce the nanostructures from the nuclei.

In one class of embodiments, the first and second precursors are reactedin the presence of a sacrificial oxide acceptor, e.g., a substrate thataccepts oxygen, e.g., a pi-acid such as triphenylphosphine or asubstituted triphenylphosphine. Without intending to be limited to anyparticular mechanism, oxide growth on the surface of growing III-Vnanocrystals can inhibit nanocrystal growth, decrease crystal quality,and/or interfere with shape control of the nanocrystals. Including anoxide acceptor in the synthesis reaction, e.g., a sacrificial andreversible oxide acceptor, can improve nanocrystal size, quality, and/orshape by promoting oxide transfer from the nanocrystal surface (e.g., byremoving phosphine oxide from the surface of InP nanocrystals). It isworth noting that, in certain embodiments, the same substance can serveas both a sacrificial oxide acceptor and as a surfactant and/orprecursor. It is also worth noting that such oxide acceptors canoptionally be included in essentially any nanostructure synthesisreaction, not only in reactions including the Group III and/or Vprecursors of the invention.

Nanostructures produced by the methods herein can be incorporated into aphotovoltaic device, LED, or nanocomposite, or can be used inessentially any other application in which semiconductor nanostructuresare desired. The nanostructures can be modified after they are produced.For example, a shell is optionally added to the nanostructures toproduce core-shell nanostructures, or any surfactant(s) coating thenanostructures can be exchanged for other surfactants or surfaceligands.

The nanostructures produced by the methods can be essentially any shapeand/or size. For example, the resulting nanostructures can includenanocrystals, substantially spherical nanocrystals, nanorods, branchednanostructures, and/or nanotetrapods. Similarly, the nanostructures cancomprise essentially any Group III-V semiconductor, including, but notlimited to, InN, InP, InAs, InSb, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs,or AlSb. The Group III-V semiconductor optionally includes more than oneGroup III and/or Group V atom; for example, the nanostructures cancomprise GaAsP or InGaAs. Thus, the methods optionally include providinga third precursor comprising a Group III or Group V atom and reacting itwith the first and/or second precursors.

As noted, nanostructure nucleation and/or growth at high temperaturescan be desirable for use of certain precursors and/or for producingcertain nanostructure shapes. Thus, one general class of embodimentsprovides high temperature methods for production of Group III-Vsemiconductor nanostructures. In the methods, a first precursor and asecond precursor are provided. The first and second precursors arereacted at a first temperature of at least 300° C. to produce thenanostructures. The first precursor comprises a trisubstituted Group Vatom, where the three substituents on the Group V atom are independentlyany alkyl group or hydrogen. The second precursor comprises a Group IIIatom.

The Group V atom can be any atom selected from Group V of the periodictable of the elements. In a preferred class of embodiments, the Group Vatom is N, P, As, Sb, or Bi.

The first precursor can include an H₃ substituted Group V atom, anH₂alkyl substituted Group V atom, or an Halkyl₂ substituted Group Vatom. In a preferred class of embodiments, the first precursor comprisesa trialkyl substituted Group V atom. The alkyl group can be, e.g.,substituted or unsubstituted and/or branched or unbranched (linear). Forexample, the first precursor can comprise a trimethyl substituted GroupV atom, a triethyl substituted Group V atom, or a tri-t-butylsubstituted Group V atom. Specific examples of first precursors include,but are not limited to, trimethylphosphine, triethylphosphine, andtri-t-butylphosphine.

The first precursor can be used in combination with essentially anysuitable second precursor, whether previously known in the art ordescribed herein. All of the features noted for the second precursorabove apply to this embodiment as well. Thus, the Group III atom can beany atom selected from Group III of the periodic table of the elements.In a preferred class of embodiments, the Group III atom is B, Al, Ga,In, or Tl. The second precursor can be a Group III inorganic compound(e.g., a Group III halide, a compound comprising one or morephosphonate, phosphinate, and/or carboxylate moieties bonded to theGroup III atom, a Group III metal oxide, or a Group III alkoxy oraryloxy). In other embodiments, the second precursor is a group IIIorganometallic compound (e.g., an alkyl metal or a trialkyl metal, or aGroup III atom substituted with three unsaturated groups, e.g., triallylindium, trivinyl indium, tributadiene indium, trialkylethynyl indium,trialkylethenyl indium, tri-4-phenylethynyl indium, ortrialkylphenylethynyl indium, a Group III atom substituted with threecyclic ketone groups, or a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups, e.g., an indiumtris-Cp compound or an indium tris-(substituted Cp) compound, e.g.,tris-cyclopentadienyl indium(III) or tris(n-hexyl cyclopentadienyl)indium(III)).

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, removal of by-product to increase nanostructure yield, use offirst and/or second surfactants, and controlling nanostructure shape byadjusting the ratio of the first and second surfactants, the ratio ofthe second surfactant and the first or second precursor, and/or theratio of the first and second precursors. It is worth noting that themolar ratio of the first precursor to the second precursor can bevaried; for example, the first precursor can be provided at a molarratio of at least 1:1, at least 2:1, at least 4:1, at least 8:1, or atleast 12:1 with respect to the second precursor.

The first temperature can be, e.g., the nucleation and/or growthtemperature. The first temperature is optionally at least 330° C., atleast 360° C., at least 380° C., at least 400° C., or at least 420° C.,e.g., as required for the particular precursor(s) used or to controlnanostructure shape or size.

Nanostructures (e.g., nanocrystals, substantially sphericalnanocrystals, nanorods, branched nanostructures, or nanotetrapods)produced by any of the methods herein form another feature of theinvention.

Compositions

Compositions related to the methods are another feature of theinvention. Thus, one general class of embodiments provides a compositionincluding a first precursor and a second precursor. The first precursorcomprises a trisubstituted Group V atom. The trisubstituted Group V atomis other than a) a trialkyl substituted Group V atom comprising anunbranched and unsubstituted alkyl group, b) an H₃ substituted Group Vatom, c) an H₂alkyl substituted Group V atom comprising an unbranchedand unsubstituted alkyl group, d) an Halkyl₂ substituted Group V atomcomprising an unbranched and unsubstituted alkyl group, or e) atris(trialkylsilyl) substituted Group V atom. In certain embodiments,first precursors of the invention optionally exclude any trialkylsubstituted, H₂alkyl substituted, or Halkyl₂ substituted Group V atom.The second precursor comprises a Group III atom.

The Group V atom can be any atom selected from Group V of the periodictable of the elements. In a preferred class of embodiments, the Group Vatom is N, P, As, Sb, or Bi.

The three substituents on the Group V atom in the first precursor can beidentical or distinct. The three substituents can be independently anyorganic group or hydrogen, for example. In one class of embodiments, thefirst precursor is a Group V organometallic compound.

In one aspect, the first precursor comprises a Group V atom substitutedwith three unsaturated groups (e.g., any group including at least onedouble or triple bond or ring, including, but not limited to, alkenyl,alkynyl, acyl, and aryl groups). For example, the first precursor can betriallylphosphine, trivinylphosphine, tributadienylphosphine,trialkylethynylphosphine, trialkylethenylphosphine,tri(4-phenylethynyl)phosphine, or trialkylphenylethynylphosphine. Asanother example, the first precursor can include a Group V atomsubstituted with three furyl or furfuryl groups; e.g., the firstprecursor can be tri-2-furylphosphine or tri-2-furfurylphosphine.

In one class of embodiments, the first precursor comprises a triacylsubstituted Group V atom. The acyl group can be, e.g., unsubstituted orsubstituted. For example, the first precursor can be a triacylphosphineor a triacylarsine, e.g., tribenzoylphosphine, trialkylbenzoylphosphine,trihexylbenzoylphosphine, trialkoylphosphine, or trihexoylphosphine. Thesubstituent optionally comprises an electron donating group or anelectron withdrawing group.

In a related class of embodiments, the first precursor comprises atriaryl substituted Group V atom. The aryl group can be, e.g.,unsubstituted or substituted. The substituent optionally comprises anelectron donating group or an electron withdrawing group. In one classof example embodiments, the first precursor comprises a tribenzylsubstituted Group V atom; for example, the first precursor can betribenzylphosphine or tribenzylarsine.

In another related class of embodiments, the first precursor comprises aGroup V atom substituted with three carboxamide groups. Thus, forexample, the first precursor can be a tricarboxamide phosphine, e.g.,N,N,N,N,N,N-hexaethylphosphine tricarboxamide.

In another class of embodiments, the first precursor comprises atrialkyl substituted Group V atom comprising a substituted and/orbranched alkyl group. For example, the first precursor can include atri-t-butyl substituted Group V atom; e.g., the first precursor can betri-t-butylphosphine.

In certain embodiments, the first precursor is a Group V inorganiccompound. For example, in one class of embodiments, the first precursorcomprises a Group V atom substituted with three carboxylate moieties orwith three phosphinate moieties. In one embodiment, the Group V atom isP such that the first precursor is a phosphite ester.

The first precursor can be present with essentially any suitable secondprecursor, whether previously known in the art or described herein (see,e.g., the examples above). The Group III atom can be any atom selectedfrom Group III of the periodic table of the elements. In a preferredclass of embodiments, the Group III atom is B, Al, Ga, In, or Tl.

In one class of embodiments, the second precursor is a Group IIIinorganic compound (e.g., a Group III halide, or a compound in which theGroup III atom is directly bonded to at least one oxygen atom or otherheteroatom, e.g., nitrogen).

In one class of embodiments, the second precursor is a Group III halide.Thus, in this class of embodiments, the second precursor is YZ₃, where Yis a Group III atom (e.g., B, Al, Ga, In, or Tl) and Z is a halogen atom(e.g., F, Cl, Br, I, or At).

In another class of embodiments, the second precursor comprises one ormore phosphonate, phosphinate, carboxylate, sulfonate, and/or boronatemoieties bonded to the Group III atom. For example, the second precursorcan comprise a bi- or tri-substituted Group III atom (e.g., atricarboxylate, bi- or tri-phosphonate, or triphosphinate substitutedGroup III atom). Thus, in one class of embodiments, the second precursoris Y(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, or Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. The alkyl or aryl group can be, e.g., substituted orunsubstituted. For example, the second precursor can be an indiumphosphonate or indium carboxylate (e.g., indium triacetate or indiumtristearate).

In yet another class of embodiments, the second precursor is a Group IIImetal oxide. For example, the second precursor can be indium oxide orgallium oxide. As another example, the second precursor can be a GroupIII alkoxy or Group III aryloxy (e.g., a Group III phenoxy, e.g., indiumphenoxy).

In one class of embodiments, instead of being a Group III inorganiccompound, the second precursor is a Group III organometallic compound.In some embodiments, the second precursor comprises a tri-substitutedGroup III atom in which the three substituents are independently anyorganic group or hydrogen. For example, the second precursor can be analkyl metal or a trialkyl metal, e.g., trimethyl indium or triethylindium. In one aspect, the second precursor comprises a Group III atomsubstituted with three unsaturated groups (e.g., any group including atleast one double or triple bond or ring, including, but not limited to,alkenyl, alkynyl, acyl, and aryl groups). For example, the secondprecursor can be triallyl indium, trivinyl indium, tributadiene indium,trialkylethynyl indium, trialkylethenyl indium, tri-4-phenylethynylindium, or trialkylphenylethynyl indium. In other embodiments, thesecond precursor comprises a Group III atom substituted with threecyclic ketone groups; for example, the second precursor can betris-alpha-cyclohexanone indium (III). In yet other embodiments, thesecond precursor comprises a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups. For example,the second precursor can be an indium tris-Cp compound or an indiumtris-(substituted Cp) compound, e.g., tris-cyclopentadienyl indium(III)or tris(n-hexyl cyclopentadienyl) indium(III).

In one class of embodiments, the first precursor comprises atrisubstituted Group V atom where the substituents are dienes, while thesecond precursor includes a trisubstituted Group III atom where thesubstituents are dienophiles. In a related class of embodiments, thefirst precursor comprises a trisubstituted Group V atom where thesubstituents are dienophiles while the second precursor includes atrisubstituted Group III atom where the substituents are dienes.

The composition optionally also includes at least one surfactant, e.g.,a first surfactant, a second surfactant, or a mixture of first andsecond surfactants. Suitable first surfactants include, but are notlimited to, tri-n-alkyl phosphines (e.g., TOP and tri-n-butyl phosphine(TBP)), tri-n-alkyl phosphine oxides (e.g., TOPO), alkyl amines (e.g.,monoalkyl amines and bialkyl amines, or trialkyl amines such astrioctylamine), and alkyl- and/or aryl-thiols\. In one class ofembodiments, the first surfactant is a C12-C30 tri-n-alkyl phosphine,e.g., tri-n-dodecyl phosphine or tri-n-hexadecyl phosphine. As notedabove, suitable first surfactants also include unsaturated Group Vderivatives; the first surfactant can comprise a Group V atomsubstituted with three unsaturated groups (e.g., alkenyl or alkynylgroups). Examples include trisalkylphenylethynylphosphines, e.g.,tri(ethynylbenzene-hexyl)phosphine,tris(ethynylbenzene-pentyl)phosphine, and the other unsaturatedphosphines noted herein. Suitable second surfactants include, but arenot limited to, alkyl amines (e.g., monoalkyl amines and bialkyl amines;typically, the first surfactant is not also an alkyl amine) andphosphonic acids (e.g., a C2-30 alkylphosphonic acid), phosphinic acids(e.g., a C2-30 bialkylphosphinic acid), carboxylic acids (e.g., a C2-30alkylcarboxylic acid), boronic acids, and sulfonic acids, as well asdeprotonated forms or condensates thereof.

Similarly, the composition optionally includes a non-coordinatingsolvent. Preferred solvents include those with a boiling point greaterthan 100° C. Suitable non-coordinating solvents include long chainalkanes or alkenes, alkane substituted aryl derivatives, and the like(including, for example, hexadecane, octadecane, octadecene,phenyldodecane, phenyltetradecane, and phenylhexadecane). Thus, in oneclass of embodiments, the non-coordinating solvent comprises an alkaneor an alkene. The non-coordinating solvent can be, e.g., hexadecane,octadecane, octadecene, phenyldodecane, phenyltetradecane, orphenylhexadecane. The composition optionally also includes a firstand/or second surfactant, e.g., such as those described herein, e.g., acarboxylic acid second surfactant. In one example embodiment, thenon-coordinating solvent is phenylhexadecane and the carboxylic acid isstearic acid. Alternatively or in addition, the composition can includea sacrificial oxide acceptor, e.g., a pi-acid such as triphenylphosphineor a substituted triphenylphosphine.

The composition is optionally maintained at a preselected temperature,for example, to facilitate nanostructure nucleation, growth, annealing,or the like. Thus, in one class of embodiments, the temperature of thecompositions is at least 250° C., at least 275° C., at least 300° C., atleast 320° C., at least 340° C., at least 360° C., at least 380° C., atleast 400° C., or at least 420° C.

The composition optionally includes one or more nuclei and/ornanostructures produced by reacting the precursors. Thus, in one classof embodiments, the composition includes one or more nanostructurescomprising the Group III atom and the Group V atom.

Essentially all of the features noted above, e.g., for type andcomposition of nanostructures produced, inclusion of a third precursor,and/or the like, apply to this embodiment as well, as relevant.

A related general class of embodiments provides a composition thatincludes a first precursor and a second precursor, where the temperatureof the composition is at least 300° C. (e.g., at least 330° C., at least360° C., at least 380° C., at least 400° C., or at least 420° C.). Thefirst precursor comprises a trisubstituted Group V atom, where the threesubstituents on the Group V atom are independently any alkyl group orhydrogen. The second precursor comprises a Group III atom.

The Group V atom can be any atom selected from Group V of the periodictable of the elements. In a preferred class of embodiments, the Group Vatom is N, P, As, Sb, or Bi.

The first precursor can include an H₃ substituted Group V atom, anH₂alkyl substituted Group V atom, or an Halkyl₂ substituted Group Vatom. In a preferred class of embodiments, the first precursor comprisesa trialkyl substituted Group V atom. The alkyl group can be, e.g.,substituted or unsubstituted and/or branched or unbranched (linear). Forexample, the first precursor can comprise a trimethyl substituted GroupV atom, a triethyl substituted Group V atom, or a tri-t-butylsubstituted Group V atom. Specific examples of first precursors include,but are not limited to, trimethylphosphine, triethylphosphine, andtri-t-butylphosphine.

The first precursor can be used in combination with essentially anysuitable second precursor, whether previously known in the art ordescribed herein. All of the features noted for the second precursorabove apply to this embodiment as well. Thus, the Group III atom can beany atom selected from Group III of the periodic table of the elements.In a preferred class of embodiments, the Group III atom is B, Al, Ga,In, or Tl. The second precursor can be a Group III inorganic compound(e.g., a Group III halide, a compound comprising one or morephosphonate, phosphinate, and/or carboxylate moieties bonded to theGroup III atom, a Group III metal oxide, or a Group III alkoxy oraryloxy). In other embodiments, the second precursor is a group IIIorganometallic compound (e.g., an alkyl metal or a trialkyl metal, aGroup III atom substituted with three unsaturated groups (e.g., triallylindium, trivinyl indium, tributadiene indium, trialkylethynyl indium,trialkylethenyl indium, tri-4-phenylethynyl indium, ortrialkylphenylethynyl indium, a Group III atom substituted with threecyclic ketone groups, or a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups, e.g., an indiumtris-Cp compound or an indium tris-(substituted Cp) compound, e.g.,tris-cyclopentadienyl indium(III) or tris(n-hexyl cyclopentadienyl)indium(III)).

The composition optionally includes one or more nuclei and/ornanostructures produced by reacting the precursors. Thus, in one classof embodiments, the composition includes one or more nanostructurescomprising the Group III atom and the Group V atom.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced and inclusion of surfactants. It is worth noting that, in oneclass of embodiments, the first surfactant is a tri-n-alkyl phosphine,for example, TOP, TBP, or a C12-C30 tri-n-alkyl phosphine (e.g.,tri-n-dodecyl phosphine or tri-n-hexadecyl phosphine). It is also worthnoting that the molar ratio of the first precursor to the secondprecursor can be varied; for example, the first precursor can be presentat a molar ratio of at least 1:1, at least 2:1, at least 4:1, at least8:1, or at least 12:1 with respect to the second precursor.

Group III Precursors

In one aspect, the invention relates to novel Group III precursors(e.g., Group III oxides, alkoxys, and aryloxys, and precursors includinga Group III atom substituted with three unsaturated groups). Methodsusing such precursors in production of Group III-V semiconductornanostructures are provided. Related methods for synthesizing and usingcertain Group III precursors are described. Compositions related to themethods are also provided.

Methods

Thus, one general class of embodiments provides methods for productionof Group III-V semiconductor nanostructures. In the methods, a firstprecursor and a second precursor are provided, and the first and secondprecursors are reacted to produce the nanostructures. The firstprecursor comprises a Group V atom. The second precursor is either aGroup III inorganic compound other than a Group III halide (e.g., InCl₃)or a Group III acetate (e.g., InAc₃), or a Group III organometalliccompound other than a trialkyl substituted Group III atom comprising anunbranched and unsubstituted alkyl group. In certain embodiments, secondprecursors of the invention optionally exclude any trialkyl substitutedGroup III atom.

The Group III atom can be any atom selected from Group III of theperiodic table of the elements. In a preferred class of embodiments, thesecond precursor comprises B, Al, Ga, In, or Tl as the Group III atom.

In one aspect, the second precursor is a Group III inorganic compound(e.g., a compound in which the Group III atom is directly bonded to atleast one oxygen atom or other heteroatom, e.g., nitrogen).

In one class of embodiments, the second precursor is a Group IIIinorganic compound comprising one or more phosphonate, phosphinate,carboxylate, sulfonate, and/or boronate moieties bonded to a Group IIIatom. For example, the second precursor can comprise a bi- ortri-substituted Group III atom (e.g., a tricarboxylate, bi- ortri-phosphonate, or triphosphinate substituted Group III atom). Thus, inone class of embodiments, the Group III inorganic compound isY(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, or Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. The alkyl or aryl group can be, e.g., substituted orunsubstituted. For example, the second precursor can be an indiumphosphonate or indium carboxylate other than indium triacetate (e.g.,indium tristearate).

In another class of embodiments, the Group III inorganic compound is aGroup III metal oxide. For example, the Group III inorganic compound canbe indium oxide or gallium oxide. As another example, the Group IIIinorganic compound can be a Group III alkoxy or Group III aryloxy (e.g.,a Group III phenoxy, e.g., indium phenoxy).

In another aspect, instead of being a Group III inorganic compound, thesecond precursor is a Group III organometallic compound. In one aspect,the second precursor comprises a Group III atom substituted with threeunsaturated groups (e.g., any group including at least one double ortriple bond or ring, including, but not limited to, alkenyl, alkynyl,acyl, and aryl groups). For example, the second precursor can betriallyl indium, trivinyl indium, tributadiene indium, trialkylethynylindium, trialkylethenyl indium, tri-4-phenylethynyl indium, ortrialkylphenylethynyl indium. In one class of embodiments, the secondprecursor comprises a Group III atom substituted with three cyclicketone groups; for example, the second precursor can betris-alpha-cyclohexanone indium (III). In other embodiments, the secondprecursor comprises a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups. For example,the second precursor can be an indium tris-Cp compound or an indiumtris-(substituted Cp) compound, for example, tris-cyclopentadienylindium(III) or tris(n-hexyl cyclopentadienyl) indium(III).

In another class of embodiments in which the second precursor is a GroupIII organometallic compound, the second precursor comprises a trialkylsubstituted Group III atom, e.g., a trialkyl substituted Group III atomcomprising a substituted and/or branched alkyl group.

The second precursor can be used in combination with essentially anysuitable first precursor, whether previously known in the art ordescribed herein. The Group V atom can be any atom selected from Group Vof the periodic table of the elements. In a preferred class ofembodiments, the Group V atom is N, P, As, Sb, or Bi.

The first precursor optionally comprises a trisubstituted Group V atom,e.g., where the Group V atom is N, P, As, Sb, or B. The threesubstituents on the Group V atom in the first precursor can be identicalor distinct. In one class of embodiments, the first precursor is a GroupV organometallic compound. The three substituents can be independentlyany organic group or hydrogen, for example.

All of the features noted for the first precursor in the embodimentsabove apply to this embodiment as well. For example, in one class ofembodiments, the first precursor comprises a Group V atom substitutedwith three unsaturated groups (e.g., the first precursor can betriallylphosphine, trivinylphosphine, tributadienylphosphine,trialkylethynylphosphine, trialkylethenylphosphine,tri(4-phenylethynyl)phosphine, or trialkylphenylethynylphosphine). Forexample, the first precursor can comprise a triacyl substituted Group Vatom. The acyl group can be, e.g., unsubstituted or substituted. Forexample, the first precursor can be a triacylphosphine or atriacylarsine, e.g., tribenzoylphosphine, trialkylbenzoylphosphine,trihexylbenzoylphosphine, trialkoylphosphine, or trihexoylphosphine. Asanother example, the first precursor can comprise a Group V atomsubstituted with three carboxamide groups (e.g., a tricarboxamidephosphine, e.g., N,N,N,N,N,N-hexaethylphosphine tricarboxamide), threefuryl groups (e.g., tri-2-furylphosphine), or three furfuryl groups(e.g., tri-2-furfurylphosphine).

In a related class of embodiments, the first precursor comprises atriaryl substituted Group V atom. The aryl group can be, e.g.,unsubstituted or substituted. The substituent optionally comprises anelectron donating group or an electron withdrawing group. In one classof example embodiments, the first precursor comprises a tribenzylsubstituted Group V atom; for example, the first precursor can betribenzylphosphine or tribenzylarsine.

In another related class of embodiments, the first precursor comprises atrialkyl substituted Group V atom. The alkyl group can be, e.g.,substituted or unsubstituted and/or branched or unbranched (linear). Forexample, the first precursor can include a trimethyl substituted Group Vatom, a triethyl substituted Group V atom, or a tri-t-butyl substitutedGroup V atom; e.g., the first precursor can be trimethylphosphine,triethylphosphine, or tri-t-butylphosphine.

In other embodiments, the first precursor comprises an H₃ substitutedGroup V atom, an Halkyl₂ substituted Group V atom, an Halkyl₂substituted Group V atom comprising a substituted and/or branched alkylgroup, an H₂alkyl substituted Group V atom, an H₂alkyl substituted GroupV atom comprising a substituted and/or branched alkyl group, or atris(trialkylsilyl) substituted Group V atom (e.g., atris(trialkylsilyl)arsine or a tris(trialkylsilyl)phosphine, e.g.,tris(trimethylsilyl)arsine or tris(trimethylsilyl)phosphine).

In certain embodiments, the first precursor is a Group V inorganiccompound. For example, in one class of embodiments, the first precursorcomprises a Group V atom substituted with three carboxylate moieties orwith three phosphinate moieties. In one embodiment, the Group V atom isP such that the first precursor is a phosphite ester.

In one class of embodiments, the first precursor comprises atrisubstituted Group V atom where the substituents are dienes, while thesecond precursor includes a trisubstituted Group III atom where thesubstituents are dienophiles. In a related class of embodiments, thefirst precursor comprises a trisubstituted Group V atom where thesubstituents are dienophiles while the second precursor includes atrisubstituted Group III atom where the substituents are dienes.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, removal of by-product to increase nanostructure yield, use offirst and/or second surfactants, non-coordinating solvents, and/orsacrificial oxide acceptors, pre-formation of a Group III-V complex,temperature, and controlling nanostructure shape by adjusting the ratioof the first and second surfactants, the ratio of the second surfactantand the first or second precursor, and/or the ratio of the first andsecond precursors.

Another general class of embodiments provides methods of producing aGroup III inorganic compound. In the methods, a first reactant and asecond reactant are provided and reacted to produce the Group IIIinorganic compound. The first reactant is a Group III halide, e.g., YZ₃,where Y is B, Al, Ga, In, or Tl and Z is F, Cl, Br, I, or At.

In a preferred class of embodiments, the second reactant is an acid,e.g., phosphonic acid, a phosphinic acid, a carboxylic acid (e.g.,stearic acid), a sulfonic acid, or a boronic acid. In certainembodiments, the acid is other than acetic acid. The resulting Group IIIinorganic compound thus, in certain embodiments, comprises one or morephosphonate, phosphinate, and/or carboxylate moieties bonded to theGroup III atom. Examples of such compounds include, but are not limitedto, Y(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, and Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. For example, the Group III inorganic compound can be indiumphosphonate or indium carboxylate (e.g., indium tristearate). In otherembodiments, the second reactant is an alcohol or an alkyl amine.

The second reactant is typically provided at a molar ratio of about 3:1with respect to the first reactant (e.g., about 2.8-3.2, about 2.9-3.1,or about 2.95-3.05). In other embodiments, the second reactant isprovided at a molar ratio of more than 3:1 with respect to the firstreactant.

A related general class of embodiments also provides methods ofproducing a Group III inorganic compound. In the methods, a firstreactant and a second reactant are provided and reacted to produce theGroup III inorganic compound. The first reactant includes a trialkylsubstituted Group III atom (e.g., B, Al, Ga, In, or Tl). The secondreactant is an acid, e.g., a phosphonic acid, a phosphinic acid, acarboxylic acid (e.g., stearic acid), a sulfonic acid, or a boronicacid. The resulting Group III inorganic compound thus, in certainembodiments, comprises one or more phosphonate, phosphinate, and/orcarboxylate moieties bonded to the Group III atom. Examples of suchcompounds include, but are not limited to, Y(alkylcarboxylate)₃,Y(arylcarboxylate)₃, Y(alkylphosphonate)₃, Y(arylphosphonate)₃,Y(alkylphosphonate)₂, Y(arylphosphonate)₂, Y(bialkylphosphinate)₃, andY(biarylphosphinate)₃, where Y is B, Al, Ga, In, or Tl. For example, theGroup III inorganic compound can be indium phosphonate or indiumcarboxylate (e.g., indium tristearate).

The second reactant is typically provided at a molar ratio of about 3:1with respect to the first reactant (e.g., about 2.8-3.2, about 2.9-3.1,or about 2.95-3.05). In other embodiments, the second reactant isprovided at a molar ratio of more than 3:1 with respect to the firstreactant.

As one specific example, reaction of trimethyl indium with threeequivalents of stearic acid yields indium tristearate and methane (whichis easily removed as a vapor).

Both general classes of methods optionally include using the resultingGroup III inorganic compound as a precursor in a nanostructure synthesisreaction. Thus, in one class of embodiments, the methods includeproviding a first precursor comprising a Group V atom and reacting theGroup III inorganic compound and the first precursor to produce GroupIII-V semiconductor nanostructures. The Group III inorganic compound isoptionally substantially isolated from any unreacted first reactantand/or second reactant prior to its reaction with the first precursor.

A group III inorganic compound produced by the methods is a feature ofthe invention. Similarly, as noted, nanostructures (e.g., nanocrystals,substantially spherical nanocrystals, nanorods, branched nanostructures,or nanotetrapods) produced by any of the methods herein form anotherfeature of the invention.

Use of such Group III inorganic compounds as precursors can beadvantageous. For example, use of these precursors can assist in shapecontrol of the resulting nanostructures. These precursors begin with theshape-controlling surfactant already bound to the metal which willcomprise the surface of the nanocrystal. As another example, reaction ofthe Group III inorganic compounds may form less reactive co-products.For example, reaction of a tribenzylphosphine first precursor with aGroup III halide second precursor produces a very reactive benzyl halideco-product, whereas reaction of the tribenzylphosphine first precursorwith a Group III phosphonate or carboxylate compound can produce a lessreactive co-product (e.g., a phosphonic or carboxylic ester,respectively).

Compositions

Compositions related to the methods are another feature of theinvention. Thus, one general class of embodiments provides a compositionincluding a first precursor comprising a Group V atom and a secondprecursor. The second precursor is either a Group III inorganic compoundother than a Group III halide (e.g., InCl₃) or a Group III acetate(e.g., InAc₃), or a Group III organometallic compound other than atrialkyl substituted Group III atom comprising an unbranched andunsubstituted alkyl group. In certain embodiments, second precursors ofthe invention optionally exclude any trialkyl substituted Group IIIatom.

The Group III atom can be any atom selected from Group III of theperiodic table of the elements. In a preferred class of embodiments, thesecond precursor comprises B, Al, Ga, In, or Tl as the Group III atom.

In one aspect, the second precursor is a Group III inorganic compound(e.g., a compound in which the Group III atom is directly bonded to atleast one oxygen atom or other heteroatom, e.g., nitrogen).

In one class of embodiments, the second precursor is a Group IIIinorganic compound comprising one or more phosphonate, phosphinate,carboxylate, sulfonate, and/or boronate moieties bonded to a Group IIIatom. For example, the second precursor can comprise a bi- ortri-substituted Group III atom (e.g., a tricarboxylate, bi- ortri-phosphonate, or triphosphinate substituted Group III atom). Thus, inone class of embodiments, the Group III inorganic compound isY(alkylcarboxylate)₃, Y(arylcarboxylate)₃, Y(alkylphosphonate)₃,Y(arylphosphonate)₃, Y(alkylphosphonate)₂, Y(arylphosphonate)₂,Y(bialkylphosphinate)₃, or Y(biarylphosphinate)₃, where Y is B, Al, Ga,In, or Tl. The alkyl or aryl group can be, e.g., substituted orunsubstituted. For example, the second precursor can be an indiumphosphonate or indium carboxylate other than indium triacetate (e.g.,indium tristearate).

In another class of embodiments, the Group III inorganic compound is aGroup III metal oxide. For example, the Group III inorganic compound canbe indium oxide or gallium oxide. As another example, the Group IIIinorganic compound can be a Group III alkoxy or Group III aryloxy (e.g.,a Group III phenoxy, e.g., indium phenoxy).

In another aspect, instead of being a Group III inorganic compound, thesecond precursor is a Group III organometallic compound. For example, inone aspect, the second precursor comprises a Group III atom substitutedwith three unsaturated groups (e.g., any group including at least onedouble or triple bond or ring, including, but not limited to, alkenyl,alkynyl, acyl, and aryl groups). For example, the second precursor canbe triallyl indium, trivinyl indium, tributadiene indium,trialkylethynyl indium, trialkylethenyl indium, tri-4-phenylethynylindium, or trialkylphenylethynyl indium. For example, in one class ofembodiments, the second precursor comprises a Group III atom substitutedwith three cyclic ketone groups; for example, the second precursor canbe tris-alpha-cyclohexanone indium (III). In other embodiments, thesecond precursor comprises a Group III atom substituted with threecyclopentadienyl or substituted cyclopentadienyl groups. For example,the second precursor can be an indium tris-Cp compound or an indiumtris-(substituted Cp) compound, for example, tris-cyclopentadienylindium(III) or tris(n-hexyl cyclopentadienyl) indium(III).

In another class of embodiments in which the second precursor is a GroupIII organometallic compound, the second precursor comprises a trialkylsubstituted Group III atom, e.g., a trialkyl substituted Group III atomcomprising a substituted and/or branched alkyl group.

The second precursor can be present with essentially any suitable firstprecursor, whether previously known in the art or described herein. TheGroup V atom can be any atom selected from Group V of the periodic tableof the elements. In a preferred class of embodiments, the Group V atomis N, P, As, Sb, or Bi.

The first precursor optionally comprises a trisubstituted Group V atom,e.g., where the Group V atom is N, P, As, Sb, or B. The threesubstituents on the Group V atom in the first precursor can be identicalor distinct. In one class of embodiments, the first precursor is a GroupV organometallic compound. The three substituents can be independentlyany organic group or hydrogen, for example.

All of the features noted for the first precursor in the embodimentsabove apply to this embodiment as well. For example, the first precursorcan include a Group V atom substituted with three unsaturated groups(e.g., the first precursor can be triallylphosphine, trivinylphosphine,tributadienylphosphine, trialkylethynylphosphine,trialkylethenylphosphine, tri(4-phenylethynyl)phosphine, ortrialkylphenylethynylphosphine). For example, the first precursor cancomprise a triacyl substituted Group V atom. The acyl group can be,e.g., unsubstituted or substituted. For example, the first precursor canbe a triacylphosphine or a triacylarsine, e.g., tribenzoylphosphine,trialkylbenzoylphosphine, trihexylbenzoylphosphine, trialkoylphosphine,or trihexoylphosphine. As another example, the first precursor cancomprise a Group V atom substituted with three carboxamide groups (e.g.,a tricarboxamide phosphine, e.g., N,N,N,N,N,N-hexaethylphosphinetricarboxamide), three furyl groups (e.g., tri-2-furylphosphine), orthree furfuryl groups (e.g., tri-2-furfurylphosphine).

In a related class of embodiments, the first precursor comprises atriaryl substituted Group V atom. The aryl group can be, e.g.,unsubstituted or substituted. The substituent optionally comprises anelectron donating group or an electron withdrawing group. In one classof example embodiments, the first precursor comprises a tribenzylsubstituted Group V atom; for example, the first precursor can betribenzylphosphine or tribenzylarsine.

In another related class of embodiments, the first precursor comprises atrialkyl substituted Group V atom. The alkyl group can be, e.g.,substituted or unsubstituted and/or branched or unbranched (linear). Forexample, the first precursor can include a trimethyl substituted Group Vatom, a triethyl substituted Group V atom, or a tri-t-butyl substitutedGroup V atom; e.g., the first precursor can be trimethylphosphine,triethylphosphine, or tri-t-butylphosphine.

In other embodiments, the first precursor comprises an H₃ substitutedGroup V atom, an Halkyl₂ substituted Group V atom, an Halkyl₂substituted Group V atom comprising a substituted and/or branched alkylgroup, an H₂alkyl substituted Group V atom, an H₂alkyl substituted GroupV atom comprising a substituted and/or branched alkyl group, or atris(trialkylsilyl) substituted Group V atom (e.g., atris(trialkylsilyl)arsine or a tris(trialkylsilyl)phosphine, e.g.,tris(trimethylsilyl)arsine or tris(trimethylsilyl)phosphine).

In certain embodiments, the first precursor is a Group V inorganiccompound. For example, in one class of embodiments, the first precursorcomprises a Group V atom substituted with three carboxylate moieties orwith three phosphinate moieties. In one embodiment, the Group V atom isP such that the first precursor is a phosphite ester.

In one class of embodiments, the first precursor comprises atrisubstituted Group V atom where the substituents are dienes, while thesecond precursor includes a trisubstituted Group III atom where thesubstituents are dienophiles. In a related class of embodiments, thefirst precursor comprises a trisubstituted Group V atom where thesubstituents are dienophiles while the second precursor includes atrisubstituted Group III atom where the substituents are dienes.

The composition optionally also includes at least one surfactant, e.g.,a first surfactant, a second surfactant, or a mixture of first andsecond surfactants. Suitable first surfactants include, but are notlimited to, tri-n-alkyl phosphines (e.g., TOP and tri-n-butyl phosphine(TBP)), tri-n-alkyl phosphine oxides (e.g., TOPO), alkyl amines (e.g.,monoalkyl amines and bialkyl amines, or trialkyl amines such astrioctylamine), and alkyl- and/or aryl-thiols. In one class ofembodiments, the first surfactant is a C12-C30 tri-n-alkyl phosphine,e.g., tri-n-dodecyl phosphine or tri-n-hexadecyl phosphine. Suitablefirst surfactants also include unsaturated Group V derivatives; thefirst surfactant can comprise a Group V atom substituted with threeunsaturated groups (e.g., alkenyl or alkynyl groups). Examples includetrisalkylphenylethynylphosphines, e.g.,tri(ethynylbenzene-hexyl)phosphine,tris(ethynylbenzene-pentyl)phosphine, and the other unsaturatedphosphines noted herein. Suitable second surfactants include, but arenot limited to, alkyl amines (e.g., monoalkyl amines and bialkyl amines;typically, the first surfactant is not also an alkyl amine) andphosphonic acids (e.g., a C2-30 alkylphosphonic acid), phosphinic acids(e.g., a C2-30 bialkylphosphinic acid), carboxylic acids (e.g., a C2-30alkylcarboxylic acid), boronic acids, and sulfonic acids, as well asdeprotonated forms or condensates thereof.

Similarly, the composition optionally includes a non-coordinatingsolvent. Preferred solvents include those with a boiling point greaterthan 100° C. Suitable non-coordinating solvents include long chainalkanes or alkenes, alkane substituted aryl derivatives, and the like(including, for example, hexadecane, octadecane, octadecene,phenyldodecane, phenyltetradecane, and phenylhexadecane). Thus, in oneclass of embodiments, the non-coordinating solvent comprises an alkaneor an alkene. The non-coordinating solvent can be, e.g., hexadecane,octadecane, octadecene, phenyldodecane, phenyltetradecane, orphenylhexadecane. The composition optionally also includes a firstand/or second surfactant, e.g., such as those described herein, e.g., acarboxylic acid second surfactant. In one example embodiment, thenon-coordinating solvent is phenylhexadecane and the carboxylic acid isstearic acid. Alternatively or in addition, the composition optionallyincludes a sacrificial oxide acceptor, e.g., a pi-acid such astriphenylphosphine.

The composition is optionally maintained at a preselected temperature,for example, to facilitate nanostructure nucleation, growth, annealing,or the like. Thus, in one class of embodiments, the temperature of thecompositions is at least 250° C., at least 275° C., at least 300° C., atleast 320° C., at least 340° C., at least 360° C., at least 380° C., atleast 400° C., or at least 420° C.

The composition optionally includes one or more nuclei and/ornanostructures produced by reacting the precursors. Thus, in one classof embodiments, the composition includes one or more nanostructurescomprising the Group V atom and a Group III atom from the Group IIIinorganic or organometallic compound.

Essentially all of the features noted above, e.g., for type andcomposition of nanostructures, inclusion of a third precursor, and/orthe like, apply to this embodiment as well, as relevant.

Another general class of embodiments provides a composition that can beused, for example, for producing a Group III inorganic compound. Thecomposition includes a first reactant and a second reactant. In oneclass of embodiments, the first reactant is a Group III halide, e.g.,YZ₃, where Y is B, Al, Ga, In, or Tl and Z is F, Cl, Br, I, or At. In arelated class of embodiments, the first reactant comprises a trialkylsubstituted Group III atom (e.g., the first reactant can be a trialkylindium, e.g., trimethyl indium). The second reactant is a phosphonicacid, a phosphinic acid, a carboxylic acid (e.g., stearic acid), asulfonic acid, a boronic acid, or an alcohol. In certain embodiments,the acid is optionally an acid other than acetic acid.

The second reactant is typically present at a molar ratio of about 3:1with respect to the first reactant (e.g., about 2.8-3.2, about 2.9-3.1,or about 2.95-3.05). In other embodiments, the second reactant isprovided at a molar ratio of more than 3:1 with respect to the firstreactant.

The composition optionally includes a Group III inorganic compoundproduced by a reaction of the first and second reactants. Thus, in oneclass of embodiments, the resulting Group III inorganic compoundcomprises one or more phosphonate, phosphinate, and/or carboxylatemoieties bonded to the Group III atom. Examples of such compoundsinclude, but are not limited to, Y(alkylcarboxylate)₃,Y(arylcarboxylate)₃, Y(alkylphosphonate)₃, Y(arylphosphonate)₃,Y(alkylphosphonate)₂, Y(arylphosphonate)₂, Y(bialkylphosphinate)₃, andY(biarylphosphinate)₃. For example, the Group III inorganic compound canbe indium phosphonate or indium carboxylate (e.g., indium tristearate).

Essentially all of the features noted above apply to this embodiment aswell, as relevant.

Nanostructure Growth at High Temperature

As noted previously, nucleation and/or growth at high temperatures maybe necessary for use of certain precursors and/or desirable forproducing certain nanostructure shapes. Thus, one general class ofembodiments provides high-temperature methods for production of GroupIII-V semiconductor nanostructures. In the methods, one or moresurfactants and/or non-coordinating solvents, a first precursorcomprising a Group V atom, and a second precursor comprising a Group IIIatom are provided. The one or more surfactants and/or non-coordinatingsolvents are heated to a first temperature. The first and secondprecursors and the one or more heated surfactants and/ornon-coordinating solvents are contacted, and the first and secondprecursors react to form nuclei capable of nucleating nanostructuregrowth. The first and second precursors, the one or more surfactantsand/or non-coordinating solvents, and the nuclei are maintained at asecond temperature which permits growth of the nuclei to produce thenanostructures; the first and second precursors react to grow thenanostructures from the nuclei. The first temperature is at least 360°C. and/or the second temperature is at least 300° C.

For example, the first temperature can be at least 380° C., at least400° C., or at least 420° C. Similarly, the second temperature can be atleast 330° C., at least 360° C., at least 380° C., at least 400° C., orat least 420° C. The first temperature can be greater than (or lessthan) the second temperature, e.g., by about 40-80° C., about 20-40° C.,about 10-20° C., about 5-10° C., or about 0-5° C., or the first andsecond temperatures can be equal.

As noted, suitable surfactants are typically liquid at the temperatureat which the nanostructures are nucleated and/or grown. Thus, in apreferred class of embodiments, each of the one or more surfactants hasa boiling point that is greater than the first and second temperatures.Similar considerations apply for any non-coordinating solvent(s).

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, Group III and V atoms, first and second precursors, andinclusion of first and/or second surfactants. It is worth noting that,in one class of embodiments, the first surfactant is a tri-n-alkylphosphine or a tri-n-alkyl phosphine oxide, for example, a C12-C30tri-n-alkyl phosphine (e.g., tri-n-dodecyl phosphine or tri-n-hexadecylphosphine).

Nanostructures (e.g., nanocrystals, substantially sphericalnanocrystals, nanorods, branched nanostructures, or nanotetrapods)produced by any of the methods herein form another feature of theinvention.

Compositions related to the methods are also provided. Thus, one generalclass of embodiments provides a composition comprising one or moresurfactants, a first precursor comprising a Group V atom, and a secondprecursor comprising a Group III atom. The temperature of thecomposition is at least 360° C. (e.g., at least 380° C., at least 400°C., or at least 420° C.). Each of the one or more surfactants preferablyhas a boiling point that is greater than the temperature of thecomposition.

The composition optionally includes one or more nuclei and/ornanostructures produced by reacting the precursors. Thus, in one classof embodiments, the composition includes one or more nanostructurescomprising the Group III atom and the Group V atom.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, Group III and V atoms, first and second precursors, andinclusion of first and/or second surfactants. It is worth noting that,in one class of embodiments, the first surfactant is a tri-n-alkylphosphine or a tri-n-alkyl phosphine oxide, for example, a C12-C30tri-n-alkyl phosphine (e.g., tri-n-dodecyl phosphine or tri-n-hexadecylphosphine).

Co-Products

Stable Co-Products

Reacting precursors to produce nanostructures typically produces boththe desired nanostructures and at least one co-product. Selectingprecursors such that the co-product is relatively stable can beadvantageous (e.g., can assist in preventing undesirable sidereactions). In one aspect, the invention provides methods ofsynthesizing nanostructures that result in production of thenanostructures and a relatively stable co-product.

Thus, one general class of embodiments provides methods for productionof Group III-V semiconductor nanostructures. In the methods, a firstprecursor comprising a Group V atom and a second precursor comprising aGroup III atom are provided and reacted to produce the nanostructuresand at least one co-product. In one class of embodiments, the co-productis an ester, a ketone, or an ether.

Reaction of a variety of combinations of first and second precursorsresults in formation of an ether, ketone, or ester. For example, whenthe first precursor comprises a trialkyl substituted Group V atom andthe second precursor comprises a tricarboxylate substituted Group IIIatom, the co-product can be an ester. As another example, the firstprecursor can comprise a triacyl substituted Group V atom, the secondprecursor a Group III atom substituted with three cyclic ketone groups(e.g., tris-alpha-cyclohexanone indium (III)), and the co-product anester (see, e.g., FIG. 2A). As yet another example, the first precursorcan comprise a triacyl substituted Group V atom, the second precursor aGroup III alkoxy or aryloxy, and the co-product an ester (see, e.g.,FIG. 2E). As yet another example, the first precursor can comprise atriacyl substituted Group V atom, the second precursor a tris-Cp ortris-(substituted Cp) Group III atom (e.g., an indium tris-Cp ortris-(substituted Cp) compound, e.g., tris-cyclopentadienyl indium(III)or tris(n-hexyl cyclopentadienyl) indium(III)), and the co-product aketone (see, e.g., FIG. 2F). As yet another example, the first precursorcan comprise triphenylphosphine or a tri-alkylphosphine, the secondprecursor tri-alkoxyindium, and the co-product an ether. See alsoExamples 7 and 8 herein.

The methods optionally include substantially purifying thenanostructures away from the co-product (e.g., prior to their use orincorporation into an optoelectronic device, a nanocomposite, or thelike). For example, an ester, ketone, or ether co-product can beevaporated using a vacuum and/or heat.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, first and second precursors, and/or the like.

Nanostructures (e.g., nanocrystals, substantially sphericalnanocrystals, nanorods, branched nanostructures, or nanotetrapods)produced by the methods form another feature of the invention.

Another general class of embodiments provides compositions related tothe methods. The composition comprises a first precursor comprising aGroup V atom, a second precursor comprising a Group III atom, ananostructure comprising the Group III atom and the Group V atom, and aco-product. In one class of embodiments, the co-product is an ester, aketone, or an ether. The nanostructure and the co-product were producedby reaction of the precursors.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, first and second precursors, co-products, and/or the like.

By-Product Removal

In one aspect, the invention provides methods for production ofnanostructures that can, e.g., increase yield of nanostructures fromnanostructure synthesis reactions through removal of a vapor by-product.In the methods, one or more precursors are provided and reacted at areaction temperature (e.g., a nanostructure growth temperature) toproduce the nanostructures and at least one by-product. The by-producthas a boiling point or sublimation temperature that is less than thereaction temperature. At least a portion of the by-product is removed asa vapor. Removal of the by-product pushes the reaction equilibriumtoward making more nano structures.

The nanostructures can be of essentially any type and/or composition.For example, the nanostructures can be semiconductor nanostructures,e.g., Group II-VI semiconductor nanostructures, Group III-Vsemiconductor nanostructures, Group IV semiconductor nanostructures,metal nanostructures, or metal oxide nanostructures.

In one class of embodiments, the one or more precursors comprise a firstprecursor comprising a group VI atom and a second precursor comprising agroup II atom. The resulting nanostructures can comprise essentially anyGroup II-group VI semiconductor, including, but not limited to, ZnS,ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS,CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, and BaTe.

In other embodiments, the one or more precursors comprise a group IVatom or a metal atom. The resulting nanostructures can compriseessentially any Group IV semiconductor, metal, or metal oxide,including, but not limited to, Ge, Si, PbS, PbSe, PbTe, Au, Ag, Co, Fe,Ni, Cu, Zn, Pd, Pt, BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃,LiTaO₃, or LiNbO₃, or an alloy or mixture thereof.

In one class of embodiments, the one or more precursors include a firstprecursor comprising a group V atom and a second precursor comprising agroup III atom. The resulting nanostructures can comprise essentiallyany Group III-V semiconductor, including, but not limited to, InN, InP,InAs, InSb, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, and AlSb.

A number of precursors and reaction temperatures can be selected suchthat the by-product formed has a boiling point or sublimationtemperature less than the reaction temperature. For example, in oneclass of embodiments, at least two precursors are reacted to form GroupIII-V semiconductor nanostructures. The first precursor comprises atrialkyl or triaryl substituted Group V atom, the second precursor is aGroup III halide, and the by-product is thus an alkyl or aryl halide.Preferably, the Group V atom is N, P, As, Sb, or Bi, and the Group IIIhalide comprises B, Al, Ga, In, or Tl and F, Cl, Br, I, or At. Exampleby-products include, but are not limited to, chlorooctane, bromooctane,benzylbromide, benzyliodide, or benzylchloride.

FIG. 3A and FIG. 3B illustrate an example reaction in which the firstprecursor is TOP, the second precursor is InCl₃, and the by-product ischlorooctane. Removal of chlorooctane, which has a boiling point of 183°C., as a vapor results in formation of more InP nanostructures (e.g.,nanocrystals).

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, inclusion of surfactant(s), precursors, and the like.

Nanostructures (e.g., nanocrystals, substantially sphericalnanocrystals, nanorods, branched nanostructures, or nanotetrapods)produced by the methods form another feature of the invention.

Another general class of embodiments provides compositions related tothe methods. The composition comprises one or more precursors,nanostructures, and at least one by-product. The by-product has aboiling point or sublimation temperature that is less than a temperatureof the composition (e.g., a nanostructure growth temperature). A portionof the by-product will therefore be a vapor.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructuresproduced, inclusion of surfactant(s), precursors, by-products, and thelike.

Surfactants

As noted above, one or more surfactants are typically used in ananostructure synthesis reaction, to assist in controlling shape and/orsize of the resulting nanostructures, to maintain solubility and preventaggregation of the nanostructures, and/or the like. A number of suitablesurfactants are described herein and known in the art and can be usedsingly or in various combinations. Examples include, but are not limitedto, tri-n-alkyl phosphines (e.g., TOP and tri-n-butyl phosphine (TBP)),tri-n-alkyl phosphine oxides (e.g., TOPO), alkyl amines (e.g., monoalkylamines and bialkyl amines, or trialkyl amines such as trioctylamine),alkyl-thiols, aryl-thiols, unsaturated Group V derivatives (e.g.,trisalkylphenylethynylphosphines, e.g.,tri(ethynylbenzene-hexyl)phosphine andtris(ethynylbenzene-pentyl)phosphine), phosphonic acids (e.g., a C2-30alkylphosphonic acid), phosphinic acids (e.g., a C2-30 bialkylphosphinicacid), carboxylic acids (e.g., a C2-30 alkylcarboxylic acid), boronicacids, and sulfonic acids. As noted, in certain embodiments, the samesubstance can serve as both a precursor and a surfactant.

A suitable surfactant (or combination of surfactants) for use with agiven set of precursors can be determined by experimentation as is knownin the art. Factors affecting choice of surfactant(s) can include, forexample, reaction temperature, choice of precursors, and desired sizeand shape of the nanostructures to be produced. For example, if thenanostructures are to be nucleated and/or grown at high temperature, thesurfactant(s) must be stable at that temperature. As another example,the relative nucleophilicity of the precursor(s) and surfactant(s) canaffect the choice of surfactant; for example, tri-n-alkyl phosphines aretypically not used as surfactants in combination with unsaturatedphosphine second (Group III) precursors. As a specific example, forreaction of a Cp₃In first precursor with a tribenzoylphosphine secondprecursor to form InP nanostructures, tri-n-alkyl phosphine surfactantscan knock the tribenzoylphosphine off of the Cp₃In coordination site,favoring the formation of Indium metal instead of InP, and are thus lessdesirable for use as surfactants with these precursors. As anotherexample, if the surfactant is capable of reacting with the firstprecursor, it is typically used in combination with a second precursorthat reacts at a lower temperature. As just one specific example, atrialkoyl phosphine can be used as the Group III precursor andtri(ethynylbenzene-hexyl)phosphine as the first surfactant, since thetrialkoyl phosphine will react at a lower temperature than thetri(ethynylbenzene-hexyl)phosphine will.

Methods and compositions including surfactants of the invention (e.g.,tri-unsaturated Group V derivatives) form a feature of the invention.Thus, one general class of embodiments provides methods for productionof nanostructures. In the methods, a surfactant comprising a Group Vatom substituted with three unsaturated groups and one or moreprecursors are provided. The one or more precursors are reacted in thepresence of the surfactant to produce the nanostructures. In one classof embodiments, the nanostructures are Group III-V semiconductornanostructures; in this class of embodiments, the one or more precursorscan, e.g., include a first precursor comprising a Group V atom and asecond precursor comprising a Group III atom.

The three unsaturated groups on the Group V atom in the surfactantoptionally comprise alkenyl or alkynyl groups. Thus, for example, thesurfactant can be a trisalkylphenylethynylphosphine, e.g.,trisalkylphenylethynylphosphine or tri(ethynylbenzene-hexyl)phosphine.

Compositions related to the methods are also a feature of the invention.One general class of embodiments provides a composition including asurfactant comprising a Group V atom substituted with three unsaturatedgroups and one or more precursors. The composition optionally alsoincludes one or more nanostructures, e.g., Group III-V semiconductornanostructures. The one or more precursors can, e.g., include a firstprecursor comprising a Group V atom and a second precursor comprising aGroup III atom.

As for the embodiments above, the three unsaturated groups on the GroupV atom in the surfactant optionally comprise alkenyl or alkynyl groups.Thus, for example, the surfactant can be atrisalkylphenylethynylphosphine, e.g., trisalkylphenylethynylphosphineor tri(ethynylbenzene-hexyl)phosphine.

Nanostructures

As noted, nanostructures (including, but not limited to, nanocrystals,substantially spherical nanocrystals, nanorods, branched nanostructures,or nanotetrapods) produced by any of the methods herein form anotherfeature of the invention, as do devices, e.g., photovoltaic devices,including such nanostructures. Since the methods do not require the useof a non-semiconducting metal catalyst to initiate nanostructure growth,the resulting nanostructures are typically free of non-semiconducting(e.g., metallic) regions. Such absence of metallic regions in thenanostructures is desirable in many applications, e.g., when thenanostructures are to avoid charge recombination.

Thus, one general class of embodiments provides a nanostructurecomprising a Group III-V semiconductor. The nanostructure issubstantially free of metallic noble, Group Ib, Group IIb, Group IIIb,and transition metal elements (e.g., such metallic elements areundetectable by a technique such as XRD). The nanostructure isoptionally substantially free of any metallic metal element (e.g., freeof metallic indium as compared to semiconducting indium phosphide).

In one class of embodiments, the nanostructure is a branchednanostructure or a nanostructure having an aspect ratio greater thanabout 1.2, and the nanostructure has a wurtzite crystal structure or azinc blende-wurtzite mixed crystal structure. For example, in one classof embodiments, the nanostructure is a nanotetrapod; nanotetrapodstypically have a zinc blende-wurtzite mixed crystal structure, with azinc blende crystal structure in their central region and a wurtzitecrystal structure in their arms. In another class of embodiments, thenanostructure is a nanorod having an aspect ratio greater than about1.2, greater than about 1.5, greater than about 2, greater than about 3,or greater than about 5. Nanorods typically have a wurtzite crystalstructure.

The Group III-V semiconductor typically comprises a first atom selectedfrom the group consisting of N, P, As, Sb, and Bi and a second atomselected from the group consisting of B, Al, Ga, In, and Tl (see, e.g.,the example materials listed above, e.g., InP and InAs).

Use of the novel precursors and/or surfactants of the invention can alsoproduce nanostructures (of any size and/or shape, including, e.g.,tetrahedral and substantially spherical nanocrystals as well as nanorodsand branched nanostructures) that are substantially free of Si (sinceSi-containing precursors need not be used), substantially free ofphosphonic acid, phosphinic acid, and/or carboxylic acid, and/orsubstantially free of tri-n-alkyl phosphines (e.g., TOP) and tri-n-alkylphosphine oxides (e.g., TOPO) (since other surfactants can be used). Useof certain precursors described herein can, e.g., result innanostructures having a sulfonic acid, or a boronic acid, or adeprotonated form or a condensate thereof, associated with a surface ofthe nanostructures. Similarly, use of certain precursors and/orsurfactants described herein can, e.g., result in nanostructures havinga carboxylic acid or a deprotonated form or a condensate thereof, and/ora surfactant comprising a Group V atom substituted with threeunsaturated groups, associated with a surface of the nanostructures.

Use of the methods and compositions of the invention can, e.g., decreaseor prevent premature termination of nanostructure growth, resulting inlarger nanostructures than were previously obtainable. Thus, forexample, one general class of embodiments provides a nanostructurecomprising a Group III-V semiconductor, the nanostructure being atetrahedral nanostructure. In one class of embodiments, thenanostructure has an edge at least 10 nm in length (e.g., at least 12nm, at least 15 nm, or at least 20 nm). All six edges are optionally atleast 10 nm in length. The nanostructure can be, e.g., a nanocrystal,and can have a zinc blende crystal structure.

Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for composition of the nanostructure. Forexample, the Group III-V semiconductor can include a first atom selectedfrom the group consisting of N, P, As, Sb, and Bi and a second atomselected from the group consisting of B, Al, Ga, In, and Tl (e.g., InPand InAs). As for the embodiments described above, the nanostructure isoptionally substantially free of metallic elements, Si, phosphonic acid,phosphinic acid, carboxylic acid, tri-n-alkyl phosphines and/ortri-n-alkyl phosphine oxides. Similarly, the nanostructure can have acarboxylic acid or a deprotonated form or a condensate thereof, and/or asurfactant comprising a Group V atom substituted with three unsaturatedgroups, associated with a surface of the nanostructure. The inventionalso includes a population of such nanostructures.

A device including a plurality of such nanostructures is also a featureof the invention, for example, a photovoltaic or other opto-electronicdevice. Packing of the tetrahedral nanostructures in such a device can,e.g., provide a favorable path for movement of electrons and/or holesthrough adjacent nanostructures disposed between opposing electrodes.Photovoltaic devices incorporating nanostructures are described, e.g.,in U.S. patent application Ser. No. 10/778,009 entitled “Nanostructureand nanocomposite based compositions and photovoltaic devices” by Scheret al.

Compositions including nanostructures and one or more Group IIIprecursor, Group V precursor, and/or surfactant of the invention arealso a feature of the invention. Thus, one general class of embodimentsprovides a composition that includes one or more nanostructures (e.g.,Group III-V semiconductor nanostructures) having a surfactant associated(covalently or non-covalently) with a surface thereof. The surfactantcomprises a Group V atom substituted with three unsaturated groups,e.g., alkenyl or alkynyl groups. Essentially all of the features notedabove apply to this embodiment as well, as relevant; e.g., for types andcomposition of nanostructures, types of surfactant, and the like. Forexample, the surfactant can be a trisalkylphenylethynylphosphine, e.g.,trisalkylphenylethynylphosphine or tri(ethynylbenzene-hexyl)phosphine.

Another general class of embodiments provides a composition thatincludes one or more Group III-V semiconductor nanostructures and afirst precursor of the invention. For example, the first precursor cancomprise a Group V atom substituted with three unsaturated groups, atriacyl substituted Group V atom, a Group V atom substituted with threecarboxamide groups, a triaryl substituted Group V atom, or a Group Vatom substituted with three carboxylate moieties or with threephosphinate moieties, for example, any such precursors described herein.For example, the first precursor can be triallylphosphine,trivinylphosphine, tributadienylphosphine, trialkylethynylphosphine,trialkylethenylphosphine, tri(4-phenylethynyl)phosphine,trialkylphenylethynylphosphine, a triacylphosphine, tribenzoylphosphine,trialkylbenzoylphosphine, trihexylbenzoylphosphine, trialkoylphosphine,trihexoylphosphine, a tricarboxamide phosphine,N,N,N,N,N,N-hexaethylphosphine tricarboxamide, tribenzylphosphine, ortribenzylarsine. As another example, the first precursor can include aGroup V atom substituted with three furyl or furfuryl groups; e.g., thefirst precursor can be tri-2-furylphosphine or tri-2-furfurylphosphine.As yet another example, the first precursor can be a phosphite ester.The composition optionally includes a second precursor, a firstsurfactant, a second surfactant, and/or a non-coordinating solvent.Essentially all of the features noted above apply to this embodiment aswell, as relevant; e.g., for types and composition of nanostructures,second precursors, first and second surfactants, solvents, sacrificialoxide acceptors, and the like.

Yet another general class of embodiments provides a composition thatincludes one or more Group III-V semiconductor nanostructures and asecond precursor of the invention. For example, the second precursor cancomprise a Group III atom which is directly bonded to at least oneoxygen atom; one or more phosphonate, phosphinate, and/or carboxylatemoieties other than an acetate moiety bonded to a Group III atom; agroup III metal oxide; a Group III alkoxy or aryloxy; or a Group IIIatom substituted with three unsaturated groups. Thus, the secondprecursor can be, e.g., indium phosphonate, indium carboxylate, indiumtristearate, indium oxide, gallium oxide, indium phenoxy, triallylindium, trivinyl indium, tributadiene indium, trialkylethynyl indium,trialkylethenyl indium, tri-4-phenylethynyl indium,trialkylphenylethynyl indium, tris-alpha-cyclohexanone indium (III), anindium tris-Cp compound, an indium tris-(substituted Cp) compound,tris-cyclopentadienyl indium(III) or tris(n-hexyl cyclopentadienyl)indium(III). The composition optionally includes a first precursor, afirst surfactant, a second surfactant, and/or a non-coordinatingsolvent. Essentially all of the features noted above apply to thisembodiment as well, as relevant; e.g., for types and composition ofnanostructures, first precursors, first and second surfactants,solvents, sacrificial oxide acceptors, and the like.

EXAMPLES

The following sets forth a series of experiments that demonstrate growthof nanostructures at high temperature, synthesis and/or use of novelGroup III and Group V precursors, use of an oxygen scavenger, andremoval of a vapor by-product, for example. It is understood that theexamples and embodiments described herein are for illustrative purposesonly and that various modifications or changes in light thereof will besuggested to persons skilled in the art and are to be included withinthe spirit and purview of this application and scope of the appendedclaims. Accordingly, the following examples are offered to illustrate,but not to limit, the claimed invention.

Example 1 Nanostructure Growth at High Temperature

A stock solution of InCl₃:THDP (stock 1) is made by heating 26.3% InCl₃by weight in tri-n-hexadecyl phosphine (THDP) to 260° C. under argon for2 hours. The stock solution is then cooled. 0.9 g of the stock solutionis added to 8 g of THDP in a 3-neck flask. The mixture is heated tobetween 360° and 400° C. Upon reaching that temperature, a 50% by weightroom temperature solution of TMS₃P (tris(trimethylsilyl)phosphine) inTOP (stock 2) is injected into the mixture. The resulting InPnanocrystals are grown at between 350° and 400° C. for between 1 and 5minutes. The reaction is then cooled to room temperature, and thenanocrystals are optionally washed or otherwise processed as desired.

Example 2 Nanostructure Synthesis Using Novel Group III and Group VPrecursors

In a 3-neck flask, 4.0 g of TOP is heated to 250° C. (flask 1). In aseparate schlenk flask, the following are combined: 240 mg InCp₃(tris-cyclopentadienyl indium(III)), 268 mg tribenzoylphosphine, and 2.0g TOP. This solution is stirred and vortexed, then injected into the TOP(flask 1) at between 250-200° C. The InP nanocrystals are grown atbetween 200 and 210° C. for 1 second to 5 minutes. The reaction is thencooled to room temperature, and the nanocrystals are optionally washedor otherwise processed as desired.

In a similar example, an acyl phosphine Group III precursor (e.g.,tribenzoylphosphine) is reacted with a Group V precursor including Insubstituted with three unsaturated groups (e.g., InCp₃) in the presenceof a non-coordinating solvent (e.g., dodecyl benzene) and a surfactantthat is an unsaturated P derivative (e.g.,tris(ethynylbenzene-pentyl)phosphine ortris(ethynylbenzene-hexyl)phosphine, which binds more weakly to thenanocrystal surface and reacts at a higher temperature than does theacyl phosphine precursor) to form InP nanocrystals. In another similarexample, an acyl phosphine Group III precursor is reacted with a Group Vprecursor including In substituted with three unsaturated groups (e.g.,InCp₃ or In-hexylCp₃) in the presence of a non-coordinating solvent, andthe acyl phosphine Group III precursor also serves as a surfactant (see,e.g., Example 7 below). Use of the non-coordinating solvent instead of atri-n-alkyl phosphine such as TOP can be advantageous, since TOP cancoordinate indium more strongly than some unsaturated (e.g., acyl)phosphines and can thus inhibit InP growth, driving the reaction toformation of indium metal instead.

Example 3 By-Product Removal

InBr₃ and TOP are combined in a 3 neck flask at a molar ratio of 12:1P:In. The flask is heated to 360° C., which is near the refluxing tempof TOP. (In this example, the maximum reaction temperature, which isgreater than 360° C., is determined by the refluxing of TOP.) Aftercolor change begins (indicating InP nanocrystal nucleation and growth),a syringe is used to remove vapor from the 3-neck flask. This vaporcontains both TOP and bromooctane (the reaction by-product). By removingthe bromooctane, the reaction to form nanocrystals increases to a fasterrate than without removal of the vapor from the flask, resulting in anincreased yield of nanocrystals in a given amount of time than withoutremoval of the vapor.

Example 4 Synthesis of Tris-Cyclopentadienyl Indium

Synthesis of tris-cyclopentadienyl indium (InCp₃) is illustrated in FIG.4 and described below. The synthesis is adapted from Beachley et al.(2002) Organometallics 21:4632.

General Methods

All manipulations were carried out with strict exclusion of air andmoisture by using Schlenk technique under an inert atmosphere of argon.A MBraun glove box was used for storage and handling of InCl₃ and LiCp.THF and toluene were dried over activated 4 A Molecular Sieves andde-gassed by three freeze-pump-thaw cycles. THF-d₈ was dried over CaH₂and after distillation was de-gassed with three freeze-pump-thaw cycles.NMR spectra were recorded with a Bruker FT NMR spectrometer at 400 MHz(¹H) or 100.6 MHz (¹³C). Indium (III) chloride, ultra dry grade, waspurchased from Alfa Aesar and used as received. LiCp was synthesized inhouse.

Procedure

In the glove box, indium (III) chloride (fwt 221.18, 3.25 g, 14.7 mmol)was transferred to a 250 mL Schlenk flask, and into a separate 250 mLSchlenk flask was transferred LiCp (fwt 72.03, 3.28 g, 45.5 mmol). About60 mL of THF was added to the InCl₃ that formed a slowly dissolvingslurry and 100 mL was added to the LiCp which formed a yellow-clearsolution. Then the LiCp solution was added intermittently to the InCl₃solution by cannula over 30 minutes with stirring. During the additionthe reaction solution turned from yellow to yellow-orange. One hourafter the addition was complete, the volatiles were removed by vacuumtransfer to about 20 mtorr which rendered the product as an orangepaste. Then 60 mL of toluene was added, and, after mixing thoroughly toinsure the chunks of paste were broken up, the supernatant wastransferred by filter tip cannula to a separate Schlenk flask. Again thevolatiles were removed by vacuum transfer to a pressure of <20 mtorr.When the solvent was removed the product became a yellowmicrocrystalline powder (fwt 310.1, 3.67 g, 11.8 mmol, 80.6% yield). Theproduct was stored in the glove box freezer at −35° C.

Analysis

¹H NMR (THF-d₈): δ 5.80 (s, C₅H₅). ¹³C {¹H} NMR (THF-d₈): δ 109.0 (s,C₅H₅).

Example 5 Synthesis of Tris-Hexylcyclopentadienyl Indium fromDicyclopentadiene

Synthesis of tris-hexylcyclopentadienyl indium (fwt 562.58) fromdicyclopentadiene via cyclopentadiene (fwt 66.10, d=0.797) andC₅H₅(CH₂)₅CH₃ (fwt 150.26) is illustrated in FIG. 4B and describedbelow.

General Methods

All manipulations were carried out with strict exclusion of air andmoisture by using Schlenk technique under an atmosphere of argon. AnMBraun glove box was used for storage and handling of InCl₃ (fwt 221.18)and the product. Hexyl iodide was distilled before use and stored in astorage flask in the dark under argon over small pieces of copper metal.Indium (III) chloride, ultra dry 99.999%, was purchased from Alfa Aesar.Dicyclopentadiene was purchased from Aldrich. The InCl₃ was opened andstored in the glove box. THF and toluene were dried over activated 4 AMolecular Sieves and de-gassed by three freeze-pump-thaw cycles. NMRchemical shift data were recorded with a Bruker FT NMR at 400 MHz for¹H, 100 MHz for ¹³C {H} and 162 MHz for ³¹P {¹H} and are listed in ppm.

Cracking of Dicyclopentadiene

Dicyclopentadiene was monomerized by cracking and distillation underinert atmosphere at atmospheric pressure. The cyclopentadiene (C₅H₆) wasdistilled into a receiver cooled in a dry ice/ethanol bath. The vaportemperature was maintained between 40 and 60° C. during thisdistillation.

Synthesis of C₅H₅(CH₂)₅CH₃

To a 1 L, 1-neck Schlenk flask with a 250 mL addition funnel was addedTHF (400 mL) and C₅H₆ (20.0 mL, 25.1 g, 0.380 mol). The reactionsolution was cooled in a dry ice/ethanol bath. Next, n-BuLi (106 mL of2.5 M, 0.265 moles) was transferred to the addition funnel and addeddropwise over 30 minutes. About 5 minutes after the addition wascomplete the dry ice/ethanol bath was removed and the reaction solutiongradually warmed to room temperature. The turbidity of the reactionsolution increased and became opaque upon warming to room temperature.Then the reaction flask was gently heated on a thermostat controlledbath at 30° C. for 30 minutes. Next the reaction solution was cooled ina dry ice/ethanol bath, and hexyl iodide (39.2 mL, 56.3 g, 0.265 moles)was dissolved in THF (50 mL) and added over 30 minutes to the reactionsolution. About 10 minutes after the addition was complete, the dryice/ethanol bath was removed and the solution warmed to roomtemperature. It was stirred at room temperature overnight. The reactionsolution was poured into 200 mL of saturated NH₄Cl and stirred for about20 minutes. Then the reaction solution was washed into a reparatoryfunnel with 200 mL of hexane, and after phase separation the organicphase was washed with water 5×100 mL. The organic phase was then washedwith brine 2×100 mL and dried over Na₂SO₄. The solvent was removed fromthe product by distillation at atmospheric pressure under argon using apot temperature (i.e. oil bath temperature) of about 90° C. and a vaportemperature between 58 to 64° C. After removal of the solvent theproduct was distilled trap-to-trap with a liquid nitrogen cooledreceiver at reduced pressure. The product was isolated as a clearcolorless oil. The yield is about 50% or 19.2 g. The product was storedin the −35° C. freezer in the glove box.

Synthesis of In[C₅H₄(CH₂)₅CH₃]₃

The reaction was set up in a 250 mL, 1-neck Schlenk flask with a 100 mLaddition funnel. On the Schlenk line THF (100 mL) and C₅H₅(CH₂)₅CH₃(6.22 g, 41.4 mmol) were added. The reaction solution was cooled in adry ice/ethanol bath and n-BuLi was added (16.5 mL, 2.5 M, 41.3 mmol)over 15 minutes. Then, 10 minutes after the addition was complete, thebath was removed and the reaction solution gradually warmed to roomtemperature. Into another 500 mL Schlenk flask InCl₃ (3.05 g, 13.8 mmol)was added in the glove box and on the Schlenk line the InCl₃ was dilutedwith THF (60 mL). The resulting solution was a slurry. About 30 minutesafter reaching room temperature the Li anion solution was added to theInCl₃/THF slurry over about 5 minutes and stirred at room temperaturefor about 30 minutes. Next, the volatiles were removed by vacuumtransfer. When the vacuum reached <50 mtorr the residue was extractedwith hexane 3×40 mL, and transferred by filter tip cannula. The filterpaper used was Whatman 5 with particle retention of >2.5 nm althoughFisherbrand filter paper with particle retention of 1-5 nm has also beenused. The organic filtrate was combined and the product isolated byremoval of the volatiles by vacuum transfer. The product is a clearorange oil (3.72 g, 3.31 mmoles, 24.0% yield) and was stored in theglove box freezer at −35° C.

Analysis of C₅H₅(CH₂)₅CH₃

¹H NMR (toluene-d₈, δ): 0.90 (t, 3H, CH₃), 1.34 (m, 6H, (CH₂)₃), 1.55(m, 2H, CH₂), 2.39 (m, 2H, CH₂), 2.88, 2.95 (m, 2H, ring CH₂), 6.01,6.15, 6.25, 4.43 (m, 3H, ring CH). IR (cm⁻¹, diamond): 3066 w br, (CHdiene), 2960 s, 2928 s, 2854 m (CH aliphatic). MALDI TOF MS (m/z): 151.3(M+H).

Analysis of In[C₅H₄(CH₂)₅CH₃]₃

¹H NMR (toluene-d₈): δ 0.90 (s, 3H, CH₃), 1.30 (m, 6H, (CH₂)₃), 1.70 (m,2H, CH₂), 2.60 (m, 2H, CH₂), 5.60, 6.10 (m, 2H, ring CH). ¹³C {¹H} NMR(toluene-d₈, 6): 14.3, 23.2, 30.0, 30.4, 32.2, 32.3 (s, (CH2)5CH3),101.0, 112.4, 137.4 (s br, CH). IR (cm-¹, diamond): 3062 w br (CH Cp),2960 s, 2928 s, 2854 m (CH aliphatic).

Example 6 SYNTHESIS OF P[COC₆H₄(CH₂)₆CH₃]₃

Synthesis of P[COC₆H₄(CH₂)₆CH₃]₃ (fwt 640.87) from Cl(CO)C₆H₄(CH₂)₆CH₃(fwt 238.75, d=0.978) is illustrated in FIG. 4C and described below. Thesynthesis is adapted from Plazek and Tyka (1959) Roczniki Chem. 33:549.It is worth noting that As precursors can be made (and used innanostructure synthesis reactions) analogously to the P precursordescribed herein.

General Methods

All manipulations were carried out with strict exclusion of air andmoisture by using Schlenk technique under an atmosphere of dry nitrogen.Pyridine, THF, toluene and toluene-d₈ were dried over activated 4 AMolecular Sieves and de-gassed by three freeze-pump-thaw cycles.Phosphine gas was purchased from Matheson Trigas and used withoutfurther purification. The acid chloride, Cl(CO)C₆H₄(CH₂)₆CH₃, wasdistilled before use (bp=100° C. at 0.1 torr) and stored in a Schlenkstorage flask under argon. Water (used in the work up) was degassed withbubbling nitrogen for >30 minutes. NMR chemical shift data were recordedwith a Bruker FT NMR at 400 MHz for ¹H, 100 MHz for ¹³C {¹H} and 162 MHzfor ³¹P {¹H} and are listed in ppm.

Synthesis of P[COC₆H₄(CH₂)₆CH₃]₃

This reaction was performed in a 1 L storage flask that has a Teflonstopper to seal the flask and Schlenk line connection attachment abovethe valve. The 1 L storage flask was connected to the Schlenk line andphosphine tank regulator using a ‘Y’ fitting on the vacuum tubing. Afterevacuation and back flush cycles, Cl(CO)C₆H₄(CH₂)₆CH₃ (12.0 mL, 11.98 g,50.1 mmol) was added to the storage flask followed by pyridine (40.6 mL,39.7 g, 501 mmol). The solution was frozen with liquid nitrogen andevacuated to <50 mtorr. After maintaining vacuum for about 1 minute, thevalve to the storage flask was closed and the hoses back flushed withargon. The reaction flask was removed from the liquid nitrogen andwarmed to room temperature (valve still closed) behind a blast shield.When the solution had warmed to room temperature, the hoses wereevacuated to <50 mtorr and the valve on the Schlenk line was closed.Next, the valve to the storage flask was opened and about 0.7 atmosphereof phosphine gas was released into the system using the phosphine tankregulator. The valve on the storage flask was then closed. The phosphinegas remaining in the hoses was decomposed by release into a bleach bath.The reaction flask was stirred at room temperature for three days.

The storage flask and 1 L Schlenk flask (with new septa) were attachedto the Schlenk line using a ‘Y’ fitting on the vacuum tubing. The hosesand Schlenk flask were evacuated to a vacuum of <50 mtorr and the valveto the Schlenk line was closed. Next, (behind a blast shield) theSchlenk flask was cooled in liquid nitrogen and the valve to thestorage/reaction flask was opened. The excess phosphine gas wascondensed in the Schlenk flask. The valve to the storage flask wasclosed. The Schlenk flask was removed from the liquid nitrogen and theflask warmed to room temperature behind a blast shield. When the Schlenkflask had warmed to room temperature, the phosphine gas was decomposedby release into a bleach bath. The storage flask (containing thereaction solution) was re-connected to the Schlenk line and thevolatiles removed by vacuum transfer to <200 mtorr. The residue wasextracted with toluene (2×20 mL and 1×10 mL) and the filtrate wastransferred by filter tip cannula to a 250 mL Schlenk flask. Thefiltrate was washed with degassed water (3×20 mL) and the volatilesremoved by vacuum transfer to produce the crude product as a viscous,clear orange oil. A high vacuum was applied at <40 mtorr while the flaskcontaining the product was gently heated in a bath to 30° C. for >12 h.The product is a waxy orange solid (8.62 g, 13.5 mmoles, 80.5% yield).It is worth noting that the product reacts quickly with oxygen butslowly with water and water is used to wash the product at the end ofthe work-up. Therefore, immediately after the majority of the volatilesare removed by vacuum transfer in the work-up a high vacuum of <40 mtorris to be applied to the product. Although the solution is viscous,traces of water are removed that would react with the product and causedecomposition.

Analysis of P[COC₆H₄(CH₂)₆CH₃]₃

¹H NMR (toluene-d₈, 6): 0.90 (t, 3H, CH₃), 1.19, 1.28 (m, 8H, CH₂), 1.38(m, 2H, CH₂), 2.35 (m, 2H, CH₂), 6.93, 8.01 (d, 4H, CH). ¹³C {¹H} NMR(toluene-d₈, 6): 14.3, 23.1, 29.6, 19.7, 31.2, 32.2, 36.3 (s,(CH₂)₆CH₃), 139.0, 130.8, 129.3 (d, Ph), 128.9 (s, Ph), 204.9 (d, C═O).³¹P {¹H} NMR (toluene-d₈, 6): 53 (s, phosphine). IR (cm⁻¹, diamond):1643 s, 1606 s (C═O), 3030 w (CH aromatic), 2956 sh, 2928 s, 2854 m (CHaliphatic). MALDI TOF MS (m/z): 641.5 (M+H).

Example 7 Synthesis of a Cyclopentadienyl Indium-Acyl Phosphine Complexand Preparation of Indium Phosphide Nanocrystals

General Methods

All manipulations were carried out with strict exclusion of air andmoisture by using Schlenk technique under an inert atmosphere of argon.Also, reagents were stored in a glove box until use. An M Braun glovebox was used for storage and handling of In(C₅H₅)₃ andP[COC₆H₄(CH₂)₆CH₃]₃. Toluene was dried over activated 4 AngstromMolecular Sieves and de-gassed by three freeze-pump-thaw cycles.Tetradecylbenzene was distilled with vapor temperature of 150 to 160° C.and pressure of <70 mtorr. P[COC₆H₄(CH₂)₆CH₃]₃ is an orange waxy solidand was stored in the glove box freezer at −35° C. NMR chemical shiftdata are listed in ppm and were recorded with a Bruker FT NMR at 400 MHzfor ¹H 100 MHz for ¹³C {¹H} and 162 MHz for ³¹P {¹H}.

Spectroscopic Evidence for Indium-Phosphine Complex Formation

Equal molar amounts In(C₅H₅)₃ and P[COC₆H₄(CH₂)₆CH₃]₃ (0.037 mmol) werecombined in an NMR tube and dissolved in toluene-d₈ in the glove box.Analysis by ³¹P {¹H} NMR for P[COC₆H₄(CH₂)₆CH₃]₃ was 53.0 ppm while forthe ‘In—P’ complex was 70.8 ppm under the same conditions. Formation ofthe In—P complex is schematically illustrated in FIG. 5A.

Synthesis of a Preformed Indium-Phosphide Precursor in Tetradecylbenzene

To a 50 mL Schlenk flask in the glove box was added In(C₅H₅)₃ (fwt310.1, 0.249 g, 0.80 mmol) and P[COC₆H₄(CH₂)₆CH₃]₃ (fwt 640.87, 0.517 g,0.80 mmol). In the glove box toluene (4.0 mL) was added and the mixturestirred for a few minutes at room temperature. To the resulting redsolution tetradecylbenzene (2.0 mL) was added. Then on the Schlenk linetoluene was removed by vacuum transfer while the solution was gentlyheated at 30° C. until the pressure reached <50 mtorr for about 5minutes duration. Preformation of the precursor complex is schematicallyillustrated in FIG. 5B.

Synthesis of Indium-Phosphide from the Preformed Precursor

Synthesis of InP nanocrystals from the preformed precursor isschematically illustrated in FIG. 5C. To a 25-mL, 3-neck round bottomflask equipped with an air reflux condenser was added tetradecylbenzene(7.0 mL) inside the glovebox. Then, on the vacuum line, the mixture washeated to 360° C. with the temperature control set to 380° C. tomaintain a constant reflux. The reaction was initiated by rapidinjection of the solution of In(C₅H₅)₃ and P[COC₆H₄(CH₂)₆CH₃]₃ intetradecylbenzene. This instantly turned the reaction solution opaqueblack. About 5 minutes later, an orange solution of P[COC₆H₄(CH₂)₆CH₃]₃(0.518 g, 0.80 mmol) in tetradecylbenzene (3.0 mL) was added by syringeover about 5 min. FIG. 5D shows the reaction temperature profile. About4 minutes later the reaction was stopped by removal of the heat from thereaction flask. When the solution temperature had dropped to about 60°C., toluene (2.0 mL) was added. Then the reaction solution wastransferred into the glove box for purification. Also a small amount ofsolid material was collected from the air reflux condenser for analysisby mass spec (FIGS. 5E1 and 5E2). The ketone with fwt 268.4 (shown atthe bottom right of FIG. 5C) was detected, suggesting simple eliminationof ligands from the preformed In—P precursor in route to forming thenanocrystal.

Indium Phosphide Nanocrystal Purification

To one quarter of the reaction solution was added isopropanol (4.0 mL)and methanol (1.0 mL). The solution was mixed with a vortex mixer anddivided into two vials. To each portion was added methanol (1.0 mL), andthe solutions were mixed again with the vortex mixer and separated bycentrifugation into two phases. The bottom phase consisted of thickblack oil. The supernatant was decanted and the black oil purifiedfurther. To the oil was added isopropanol (4.0 mL), the solutions weremixed with a vortex mixer, and solids were separated by centrifugation.Decantation produced a black oily solid that was purified further.Again, to the precipitate was added methanol (2.0 mL), the solution wasmixed with a vortex mixer and the solids separated by centrifugation.After decantation a black solid was obtained that was analyzed by TEM(FIG. 5F) and XRD (FIG. 5G). TEM samples were prepared by dissolvingpart of the black solid precipitate in a dilute solution of toluene andevaporating it onto an amorphous carbon (<10 nm thick) coated coppermesh TEM grid. They were then measured on a FEI Tecnai 12 TEM with aTwin objective lens at 120 kV. For Powder X-ray diffraction (XRD),samples were dried to a powder on a quartz plate and run in a Bruker-AXSDiscover D8 diffractometer with a general area detector diffractionsystem (GADDS). The x-ray source was Cu Kα radiation with a wavelengthof 1.540598 Å. Theoretical lines were calculated using standard unitcell dimensions.

Example 8 Synthesis of Indium Phosphide Nanocrystals fromtris-hexylcyclopentadienyl indium and P[COC₆H₄(CH₂)₆CH₃]₃

General Methods

All manipulations were carried out with strict exclusion of air andmoisture by using Schlenk technique under an inert atmosphere of argon.Also, reagents were stored in a glove box until use. An M Braun glovebox was used for storage and handling of In[C₅H₄(CH₂)₅CH₃]₃ andP[COC₆H₄(CH2)₆CH₃]₃. Toluene was dried over activated 4 AngstromMolecular Sieves and de-gassed by three freeze-pump-thaw cycles.Hexadecylbenzene was distilled with a vapor temperature between 130 and140° C. and pressure of <20 mtorr. Triphenylphosphine was degassedbriefly in the glove box antechamber. Stearic acid was dried anddegassed in a desiccator containing P₂O₅ under static vacuum for morethan 12 hours. In[C₅H₄(CH₂)₅CH₃]₃ is an orange oil andP[COC₆H₄(CH₂)₆CH₃]₃ is an orange waxy solid. Both were stored in theglove box freezer at −35° C. NMR chemical shift data are listed in ppmand were recorded with a Bruker FT NMR at 400 MHz for ¹H 100 MHz for ¹³C{¹H} and 162 MHz for ³¹P {¹H}.

Synthesis of a Preformed Indium-Phosphide Precursor Complex inHexadecylbenzene

A Schlenk flask was charged with In[C₅H₄(CH₂)₅CH₃]₃ (fwt 562.58, 0.2248g, 0.40 mmol) and P[COC₆H₄(CH₂)₆CH₃]₃ (fwt 640.87, 0.2565 g, 0.40 mmol)inside the glove box. Toluene (4.0 mL) was added and the mixture stirredat room temperature for a few minutes while a red homogeneous solutionformed. Hexadecylbenzene (2.0 mL) was added and the solution stirred atroom temperature for 30 min. Then the toluene was removed by vacuumtransfer while the solution was gently heated at 30° C. until thepressure reached <50 mtorr for a duration of about 5 minutes. Formationof the In—P precursor complex is schematically illustrated in FIG. 6A.Additionally, two Schlenk flasks were also used to prepare two othersolutions. In the glove box, one of the Schlenk flasks was charged withP[COC₆H₄(CH₂)₆CH₃]₃ (0.2574 g, 0.4 mmol) followed by toluene (4.0 mL)and after mixing briefly hexadecylbenzene (2.0 mL). To the other Schlenkflask was added In[C₅H₄(CH₂)₅CH₃]₃ (0.2264 g, 0.4 mmol) followed bytoluene (4.0 mL) and after mixing hexadecylbenzene (2.0 mL). Then thetoluene was removed from both solutions by vacuum transfer. Thesolutions were heated at 30° C. until the pressure reached <50 mtorr forabout 5 minutes duration.

Synthesis of Indium Phosphide Nanocrystals

To a 25-mL, 3-neck round bottom flask equipped with an air refluxcondenser was added triphenylphosphine (0.1044 g, 0.40 mmol), stearicacid (0.1135 g, 0.40 mmol) and hexadecylbenzene (7.0 mL) inside theglove box. (Without limitation to any particular mechanism, thetriphenylphosphine can act as a sacrificial oxide acceptor during thenanocrystal synthesis reaction, and the stearic acid can act as asurfactant and/or can attack and remove any COC₆H₄(CH₂)₆CH₃ substituentsremaining on the surface of the growing nanocrystal.) On the Schlenkline the reaction solution was heated to 385° C. under Argon. Then thereaction was initiated by addition of the complex of In[C₅H₄(CH2)₅CH₃]₃and P[COC₆H₄(CH₂)₆CH₃]₃ in hexadecylbenzene. Upon addition the reactionsolution instantly turned opaque black. Then immediately following thataddition the temperature control was reset to 330° C. About 5 min lateran orange solution of P[COC₆H₄(CH₂)₆CH₃]₃ in hexadecylbenzene was addedby a syringe pump over a period of 5 min. About 10 min after the initialinjection, the addition of P[COC₆H₄(CH₂)₆CH₃]₃ was complete and theaddition of In[C₅H₄(CH₂)₅CH₃]₃ in hexadecylbenzene was started. Thataddition occurred over a period of about 10 minutes. Next, heating at330° C. was continued for 40 minutes longer before the heat source onthe reaction flask was removed to stop the reaction. The total reactiontime was about 60 min. The reaction profile is shown in FIG. 6B. As thetemperature of the reaction solution reached 60° C., toluene (2.0 mL)was added and the reaction solution was taken into the glove box forpurification.

Indium Phosphide Nanocrystal Purification

The reaction solution was divided into four equal portions and separatedby centrifugation. The top phase was retained for further purificationand the precipitate was discarded. One of these four portions waspurified by addition of isopropanol (3.0 mL) and methanol (1.0 mL) andthe solution mixed with a vortex mixer and separated by centrifugation.After decantation the black bottom phase was dissolved in isopropanol(2.0 mL) and methanol (2.0) mL. Next, the solution was mixed with avortex mixer and separated by centrifugation leaving a black bottomphase that was purified further after decantation. Methanol (4.0 mL) wasadded and the solution was mixed with a vortex mixer and separated bycentrifugation. After decantation the bottom phase was added toisopropanol (4.0 mL) and the solution mixed with a vortex mixer andseparated by centrifugation leaving a solid bottom phase. Afterdecantation the bottom phase was added to toluene (0.5 mL) andisopropanol (4.0 mL) and the solution was mixed with a vortex mixer andseparated by centrifugation. After decantation the solid bottom phasewas added to toluene (0.5 mL) and methanol (4.0 mL) and the solution wasmixed with a vortex mixer and separated by centrifugation. Afterdecantation the solid bottom phase was added to toluene (0.5 mL) andmethanol (4.0 mL) and the solution was mixed with a vortex mixer andseparated by centrifugation. After decantation the black solid materialwas analyzed by TEM (FIG. 6C and FIG. 6D), XRD (FIG. 6E) and UV-Visspectroscopy (FIG. 6F). TEM and XRD were performed basically asdescribed in Example 7.

Example 9 Size and Shape Control of INP Nanocrystal Synthesis

Except as indicated, nanocrystals were produced basically as describedin Example 8. Indium phosphide nanocrystals were synthesized fromtris-hexylcyclopentadienyl indium (also indicated as In[C₅H₄(CH₂)₅CH₃]₃or In(CpC₆H₁₃)₃) and P[COC₆H₄(CH₂)₆CH₃]₃ (also indicated asP(COPhC₇H₁₅)₃) as illustrated in the reaction profile shown in FIG. 7A.0.4 mmol of [In(CpC₆H₁₃)₃₋P(COC₆H₄C₇H₁₅)₃] in 2.0 mL hexadecylbenzene(HDB) was injected into a mixture containing 0.4 mmol triphenylphosphine(PPh₃), 0.4 mmol stearic acid, and 7.0 ml HDB. About five minutes later,0.4 mmol of [In(CpC₆H₁₃)₃₋P(COC₆H₄C₇H₁₅)₃] in 2.0 mL HDB was added over10 minutes.

Dynamic light scattering data showing the size of the resulting InP zincblende tetrahedral nanostructures are shown in FIG. 7B. The UV-visibleabsorption spectrum of the nanocrystals is shown in FIG. 7C; the InPband edge is indicated by an arrow. Transmission electron micrographs ofthe tetrahedral nanocrystals are shown in FIG. 7D1 and FIG. 7D2. XRDanalysis (FIG. 7E) shows a clean indium phosphide zinc blende pattern(theoretical lines are indicated by squares).

Adjusting precursor complex concentrations in the precursor additionsequence can produce larger tetrahedra, e.g., as follows. Indiumphosphide nanocrystals were synthesized as illustrated in the reactionprofile shown in FIG. 7F. 0.2 mmol of [In(CpC₆H₁₃)₃₋P(COC₆H₄C₇H₁₅)₃] in2.0 mL hexadecylbenzene (HDB) was injected into a mixture containing 0.4mmol triphenylphosphine (PPh₃), 0.4 mmol stearic acid, and 7.0 ml HDB.About five minutes later, 0.6 mmol of [In(CpC₆H₁₃)₃₋P(COC₆H₄C₇H₁₅)₃] in2.0 mL HDB was added over 10 minutes. The UV-visible absorption spectrumof the resulting nanocrystals is shown in FIG. 7G. The spectrum showsmore absorption near 800 nm, indicating larger size InP nanocrystals(arrow). TEM (FIG. 7H1 and FIG. 7H2) confirms the increased size of theInP tetrahedra. Theoretical and experimental InP zinc blend XRD patternsare shown in FIG. 7I.

Example 10 Triphenylphosphine Acts as an Oxygen Scavenger inNanostructure Synthesis Reactions

Triphenylphosphine is known as an oxide acceptor in reactions such asthe Mitsunobu reaction (see Nagasawa and Mitsunobu (1981) Bull. Chem.Soc. Japan 54:2223). We have demonstrated that it can also act as anoxide acceptor in nanostructure synthesis reactions. An example reactionis schematically illustrated in FIG. 8A and FIG. 8B. MALDI TOF mass specanalysis of InP nanocrystal reaction mixtures (FIG. 8D and FIG. 8E);background matrix scan is shown in FIG. 8C reveals the presence oftriphenylphosphine oxide, supporting the hypothesis thattriphenylphosphine acts as an oxygen scavenger in nanocrystal synthesisreactions.

Example 11 Synthesis of Indium Tristearate and Use in InP NanostructureSynthesis

Trimethyl indium was reacted with three equivalents of stearic acid,yielding indium tristearate (and three equivalents of methane, whichwere evaporated). Two equivalents of (TMS)₃P were added to react withthe indium tristearate. The solvent was dodecylbenzene, and stearic acidserved as the surfactant. The resulting InP nanocrystals were analyzedby UV-visible spectroscopy (FIG. 9A); fl-final indicate successivefractions removed from the growth solution over the course of thesynthesis) and XRD (FIG. 9B).

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, it will be clear to one skilledin the art from a reading of this disclosure that various changes inform and detail can be made without departing from the true scope of theinvention. For example, all the techniques and apparatus described abovecan be used in various combinations. All publications, patents, patentapplications, and/or other documents cited in this application areincorporated by reference in their entirety for all purposes to the sameextent as if each individual publication, patent, patent application,and/or other document were individually indicated to be incorporated byreference for all purposes.

What is claimed is:
 1. A nanostructure, comprising: a Group III-Vsemiconductor; the nanostructure being substantially free of metallicnoble, Group Ib, Group IIb, Group IIIb, and transition metal elements;the nanostructure being a branched nanostructure or having an aspectratio greater than about 1.2; and the nanostructure having a wurtzitecrystal structure or a zinc blende-wurtzite mixed crystal structure. 2.The nanostructure of claim 1, wherein one or more nanostructures arenanocrystals, nanorods, or nanotetrapods.
 3. The nanostructure of claim1, wherein the aspect ratio is greater than 1.5.
 4. The nanostructure ofclaim 1, wherein the nanostructures comprise an atom selected from thegroup consisting of N, P, As, Sb, and Bi.
 5. The nanostructure of claim1, wherein the nanostructures comprise an atom selected from the groupconsisting of B, Al, Ga, In, and Ti.
 6. The nanostructure of claim 1,wherein the nanostructures are substantially free of Si, phosphonicacid, phosphinic acid, carboxylic acid, tri-n-alkyl phosphines, and/ortri-n-alkyl phosphine oxides.
 7. The nanostructure of claim 1, wherein asurface of the nanostructures is associated with a sulfonic acid, aboronic acid, or a deprotonated form or condensate thereof.
 8. Thenanostructure of claim 2, wherein a surface of the nanostructures isassociated with a carboxylic acid or a deprotonated form or condensatethereof, and/or a surfactant comprising of a Group V atom substitutedwith three unsaturated groups.
 9. A nanostructure, comprising: a GroupIII-V semiconductor; the nanostructure being substantially free ofmetallic noble, Group Ib, Group IIb, Group IIIb, and transition metalelements; the nanostructure being a tetrahedral nanostructure with allsix edges having a length of at least 10 nm; and the nanostructure beinga nanocrystal or is a zinc blende-mixed crystal structure.
 10. Thenanostructure of claim 9, wherein the nanostructures comprise an atomselected from the group consisting of N, P, As, Sb, and Bi.
 11. Thenanostructure of claim 9, wherein the nanostructures comprise an atomselected from the group consisting of B, Al, Ga, In, and Ti.
 12. Thenanostructure of claim 9, wherein the nanostructures are substantiallyfree of Si, phosphonic acid, phosphinic acid, carboxylic acid,tri-n-alkyl phosphines, and/or tri-n-alkyl phosphine oxides.
 13. Thenanostructure of claim 9, wherein a surface of the nanostructures isassociated with a sulfonic acid, a boronic acid; or a deprotonated formor condensate thereof.
 14. The nanostructure of claim 12, wherein asurface of the nanostructures is associated with a carboxylic acid or adeprotonated form or condensate thereof, and/or a surfactant comprisingof a Group V atom substituted with three unsaturated groups.